Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0

毫无疑问,随着互联网、移动网络接入成本的降低,互联网正在日益深入地走入我们的生活,越来越成为人们获取信息的高效平台,ICP行业也顺势呈现出强劲的成长趋势,成为互联网迅猛发展形势下最大的受益者,也直接促成了从web1.0到web2.0以及社区、博客、视频等一系列互联网时代的更迭和运营模式的变动。

  但是随着各站点访问量和信息交流量的迅猛增长,如何使用最小的资源成本,提高网络的效率,最优化用户体验,已经成为网络管理人员不得不面对的挑战。

  从技术上讲,就是ICP行业面临的网络资源有效利用问题,也就是如何进行对网络的访问分流,以便能够快速响应用户反应,即:负载均衡。

  从这篇文章起,我们将讲述在负载均衡技术实现中的核心技术:负载均衡算法(算法)的原理及其实现,使大家对负载均衡底层技术有一个深刻的了解。这些算法是负载均衡设备中的核心实现基础。

  本篇文章先讲述轮询调度算法 (Round-Robin)及其在此基础上改进型的权重轮询算法 (Weighted Round-Robin)。

  轮询调度算法(Round-Robin Scheduling)

  轮询调度算法的原理是每一次把来自用户的请求轮流分配给内部中的服务器,从1开始,直到N(内部服务器个数),然后重新开始循环。

  算法的优点是其简洁性,它无需记录当前所有连接的状态,所以它是一种无状态调度。

  轮询调度算法流程

  假设有一组服务器N台,S = {S1, S2, …, Sn},一个指示变量i表示上一次选择的服务器ID。变量i被初始化为N-1。其算法如下:

j = i;

do

{

j = (j + 1) mod n;

i = j;

return Si;

} while (j != i);

return NULL;

  这种算法的逻辑实现如图1所示:

  

                                             图1 轮询调度实现逻辑图示

  轮询调度算法假设所有服务器的处理性能都相同,不关心每台服务器的当前连接数和响应速度。当请求服务间隔时间变化比较大时,轮询调度算法容易导致服务器间的负载不平衡。

  所以此种均衡算法适合于服务器组中的所有服务器都有相同的软硬件配置并且平均服务请求相对均衡的情况。

 

 

权重轮询调度算法(Weighted Round-Robin Scheduling)

  上面所讲的轮询调度算法并没有考虑每台服务器的处理能力,在实际情况中,可能并不是这种情况。由于每台服务器的配置、安装的业务应用等不同,其处理能力会不一样。所以,我们根据服务器的不同处理能力,给每个服务器分配不同的权值,使其能够接受相应权值数的服务请求。

  权重轮询调度算法流程

  假设有一组服务器S = {S0, S1, …, Sn-1},W(Si)表示服务器Si的权值,一个指示变量i表示上一次选择的服务器,指示变量cw表示当前调度的权值,max(S)表示集合S中所有服务器的最大权值,gcd(S)表示集合S中所有服务器权值的最大公约数。变量i初始化为-1,cw初始化为零。其算法如下:

 

while (true) {

  i = (i + 1) mod n;

  if (i == 0) {

     cw = cw - gcd(S);

     if (cw <= 0) {

       cw = max(S);

       if (cw == 0)

         return NULL;

     }

  }

  if (W(Si) >= cw)

    return Si;

}

  这种算法的逻辑实现如图2所示,图中我们假定四台服务器的处理能力为3:1:1:1。

  

                                        图2 权重轮询调度实现逻辑图示

  由于权重轮询调度算法考虑到了不同服务器的处理能力,所以这种均衡算法能确保高性能的服务器得到更多的使用率,避免低性能的服务器负载过重。所以,在实际应用中比较常见。

  总结

  轮询调度算法以及权重轮询调度算法的特点是实现起来比较简洁,并且实用。目前几乎所有的负载均衡设备均提供这种功能。

----------------------------------

一:原理:

linux操作系统下双网卡绑定有七种模式。现在一般的企业都会使用双网卡接入,这样既能添加网络带宽,同时又能做相应的冗余,可以说是好处多多。而一般企业都会使用linux操作系统下自带的网卡绑定模式,当然现在网卡产商也会出一些针对windows操作系统网卡管理软件来做网卡绑定(windows操作系统没有网卡绑定功能 需要第三方支持)。进入正题,linux有七种网卡绑定模式:0. round robin,1.active-backup,2.load balancing (xor),  3.fault-tolerance (broadcast), 4.lacp,  5.transmit load balancing, 6.adaptive load balancing。

二:案例一mode=1(active-backup):一个网卡处于活动状态 ,一个处于备份状态,所有流量都在主链路上处理。当活动网卡down掉时,启用备份的网卡。

1:[root@lyt ~]# vim /etc/sysconfig/network-scripts/ifcfg-eth0           #编辑该设备eth0如图:

image

[root@lyt ~]# vim /etc/sysconfig/network-scripts/ifcfg-eth1            #编辑该设备eth1 如图:

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第1张图片

2:[root@lyt ~]# cd /etc/sysconfig/network-scripts/

[root@lyt network-scripts]# cp ifcfg-eth0  ifcfg-bond0        #生成一个bond0的虚拟网卡

[root@lyt network-scripts]# vim ifcfg-bond0        #编辑该网卡内容

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第2张图片

3:[root@lyt network-scripts]# vim /etc/modprobe.conf       #编辑该配置文件

下图中1表示系统在启动时加载bonding模块,对外虚拟网络接口设备为 bond0;miimon=100表示系统每100ms监测一次链路连接状态,如果有一条线路不通就转入另一条线

路;mode=1表示fault-tolerance (active-backup)提供冗余功能,工作方式是主备的工作方式,也就是说默认情况下只有一块网卡工作,另一块做备份。

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第3张图片

options bond0 miimon=100 mode=1

4:[root@lyt network-scripts]# vim /etc/rc.local        #编辑该开机脚本,将eth0和eth1网卡进行绑定

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第4张图片

5:[root@lyt network-scripts]# init 6       #重启,bond0启动成功

image

[root@lyt ~]# ifconfig      #查看网卡信息,在此处三块网卡的mac地址是一样的

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第5张图片

[root@lyt ~]#vim /proc/net/bonding/bond0      #查看模式及网卡信息。实际mac地址是不一样的

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第6张图片

测试:

6:Xshell:\> ping 192.168.101.50  –t      #一直测试网络的连通性查看结果

断掉eth0网卡后显示结果

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第7张图片

将网卡eth0断掉后,系统使用备份网卡eth1,此时eth1处于活动状态

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第8张图片

案例二:mode=0(round robin):所有链路处于负载均衡状态,这模式的特点增加了带宽,同时支持容错能力。

1:在案例一的基础上,只需要修改/etc/modprobe.conf 配置文件:如图:

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第9张图片

2:vim /proc/net/bonding/bond0        #查看使用的模式及网卡信息,如图:

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第10张图片

测试:mode=0:

3:Xshell:\> ping 192.168.101.50 –t #一直测试网络的连通性查看结果

将网卡eth1断掉后,系统依然可以ping通

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第11张图片

Round-Robin负载均衡算法及其实现原理& Linux下双网卡绑定bond0_第12张图片

 -------------------------------------------------

eth file

 

The /etc/sysconfig/network-scripts/ifcfg-ethN files

File configurations for each network device you may have or want to add on your system are located in the/etc/sysconfig/network-scripts/ directory with Red Hat Linux 6.1 or 6.2 and are namedifcfg-eth0 for the first interface and ifcfg-eth1 for the second, etc. Following is a example/etc/sysconfig/network-scripts/ifcfg-eth0 file:

           DEVICE=eth0
           IPADDR=208.164.186.1
           NETMASK=255.255.255.0
           NETWORK=208.164.186.0
           BROADCAST=208.164.186.255
           ONBOOT=yes
           BOOTPROTO=none
           USERCTL=no
           

If you want to modify your network address manually, or add a new network on a new interface, edit this file -ifcfg-ethN, or create a new one and make the appropriate changes.

  • DEVICE=devicename, where devicename is the name of the physical network device.

  • IPADDR=ipaddr, where ipaddr is the IP address.

  • NETMASK=netmask, where netmask is the netmask IP value.

  • NETWORK=network, where network is the network IP address.

  • BROADCAST=broadcast, where broadcast is the broadcast IP address.

  • ONBOOT=answer, where answer is yes or no. Do the interface need to be active or inactive at boot time.

  • BOOTPROTO=proto, where proto is one of the following :

    1. none - No boot-time protocol should be used.

    2. bootp - The bootp now pump protocol should be used.

    3. dhcp - The dhcp protocol should be used.

USERCTL=answer, where answer is one of the following:

  1. yes - Non-root users are allowed to control this device.

  2. no - Only the super-user root is allowed to control this device

 

------------------------------------------------------------

RHEL: Linux Bond / Team Multiple Network Interfaces (NIC) Into a Single Interface

by nixCraft onApril 3, 2006 ·113 comments·Last updatedSeptember 4, 2011

Finally, today I had implemented NIC bounding (bind both NIC so that it works as a single device). Bonding is nothing but Linux kernel feature that allows to aggregate multiple like interfaces (such as eth0, eth1) into a single virtual link such as bond0. The idea is pretty simple get higher data rates and as well as link failover. The following instructions were tested on:

  1. RHEL v4 / 5 / 6 amd64
  2. CentOS v5 / 6 amd64
  3. Fedora Linux 13 amd64 and up.
  4. 2 x PCI-e Gigabit Ethernet NICs with Jumbo Frames (MTU 9000)
  5. Hardware RAID-10 w/ SAS 15k enterprise grade hard disks.
  6. Gigabit switch with Jumbo Frame

This server act as an heavy duty ftp, and nfs file server. Each, night a perl script will  transfer lots of data from this box to a backup server. Therefore, the network would be setup on a switch using dual network cards. I am using Red Hat enterprise Linux version 4.0. But, the inductions should work on RHEL 5 and 6 too.

Say Hello To bounding Driver

Linux allows binding of multiple network interfaces into a single channel/NIC using special kernel module called bonding. According to official bondingdocumentation:

The Linux bonding driver provides a method for aggregating multiple network interfaces into a single logical "bonded" interface. The behavior of the bonded interfaces depends upon the mode; generally speaking, modes provide either hot standby or load balancing services. Additionally, link integrity monitoring may be performed.

Step #1: Create a Bond0 Configuration File

Red Hat Enterprise Linux (and its clone such as CentOS) stores network configuration in /etc/sysconfig/network-scripts/ directory.  First, you need to create a bond0 config file as follows:
# vi /etc/sysconfig/network-scripts/ifcfg-bond0
Append the following linest:

 
DEVICE=bond0
IPADDR=192.168.1.20
NETWORK=192.168.1.0
NETMASK=255.255.255.0
USERCTL=no
BOOTPROTO=none
ONBOOT=yes
 

You need to replace IP address with your actual setup. Save and close the file.

Step #2: Modify eth0 and eth1 config files

Open both configuration using a text editor such as vi/vim, and make sure file read as follows for eth0 interface
# vi /etc/sysconfig/network-scripts/ifcfg-eth0
Modify/append directive as follows:
DEVICE=eth0
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none

Open eth1 configuration file using vi text editor, enter:
# vi /etc/sysconfig/network-scripts/ifcfg-eth1
Make sure file read as follows for eth1 interface:
DEVICE=eth1
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none

Save and close the file.

Step # 3: Load bond driver/module

Make sure bonding module is loaded when the channel-bonding interface (bond0) is brought up. You need to modify kernel modules configuration file:# vi /etc/modprobe.conf
Append following two lines:alias bond0 bonding
options bond0 mode=balance-alb miimon=100

Save file and exit to shell prompt. You can learn more about all bounding options by clickinghere).

Step # 4: Test configuration

First, load the bonding module, enter:
# modprobe bonding
Restart the networking service in order to bring up bond0 interface, enter:
# service network restart
Make sure everything is working. Type the following cat command to query the current status of Linux kernel bounding driver, enter:
# cat /proc/net/bonding/bond0
Sample outputs:

Bonding Mode: load balancing (round-robin)
MII Status: up
MII Polling Interval (ms): 100
Up Delay (ms): 200
Down Delay (ms): 200
Slave Interface: eth0
MII Status: up
Link Failure Count: 0
Permanent HW addr: 00:0c:29:c6:be:59
Slave Interface: eth1
MII Status: up
Link Failure Count: 0
Permanent HW addr: 00:0c:29:c6:be:63

To kist all network interfaces, enter:
# ifconfig
Sample outputs:

bond0     Link encap:Ethernet  HWaddr 00:0C:29:C6:BE:59
 inet addr:192.168.1.20  Bcast:192.168.1.255  Mask:255.255.255.0
 inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link
 UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1
 RX packets:2804 errors:0 dropped:0 overruns:0 frame:0
 TX packets:1879 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:0
 RX bytes:250825 (244.9 KiB)  TX bytes:244683 (238.9 KiB)
eth0      Link encap:Ethernet  HWaddr 00:0C:29:C6:BE:59
 inet addr:192.168.1.20  Bcast:192.168.1.255  Mask:255.255.255.0
 inet6 addr: fe80::20c:29ff:fec6:be59/64 Scope:Link
 UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
 RX packets:2809 errors:0 dropped:0 overruns:0 frame:0
 TX packets:1390 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:1000
 RX bytes:251161 (245.2 KiB)  TX bytes:180289 (176.0 KiB)
 Interrupt:11 Base address:0x1400
eth1      Link encap:Ethernet  HWaddr 00:0C:29:C6:BE:59
 inet addr:192.168.1.20  Bcast:192.168.1.255  Mask:255.255.255.0
 inet6 addr: fe80::20c:29ff:fec6:be59/64 Scope:Link
 UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
 RX packets:4 errors:0 dropped:0 overruns:0 frame:0
 TX packets:502 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:1000
 RX bytes:258 (258.0 b)  TX bytes:66516 (64.9 KiB)
 Interrupt:10 Base address:0x1480

 

-------------------------------------

How many slaves can a bonding device have? OR Can you bond more than 2 nics?
This is limited only by the number of network interfaces (NIC) Linux supports and/or the number of network cards you can place in your system

-----------------------

Understanding NIC Bonding with Linux       

NIC bonding with Linux is simple, once you understand all your choices and their limitations.

            By Charlie Schluting | Dec 2, 2009                   

Network card bonding is an effective way to increase the available bandwidth, if it is done carefully. Without a switch that supports 802.3ad, you must have the right hardware to make it work. In this article we will explain how bonding works so you can deploy the right mode for your situation.

Most administrators assume that bonding multiple network cards together instantly results in double the bandwidth and high-availability in case a link goes down. Unfortunately, this is not true. Let's start with the most common example, where you have a server with high network load, and wish to allow more than 1Gb/s.

Bonding With 802.3Ad

You connect two interfaces to your switch, enable bonding, and discover half your packets are getting lost. If Linux is configured for 802.3ad link aggregation, the switch must also be told about this. In the Cisco world, this is called an EtherChannel. Once the switch knows those two ports are actually supposed to use 802.3ad, it will load balance the traffic destined for your attached server.

This works great if a large number of network connections from a diverse set of clients are connecting. If, however, the majority of the throughput is coming from a single server, you won't get better than the 1Gb/s port speed. Switches are load balancing based on the source MAC address by default, so if only one connection takes place, it always gets sent down the same link. Many switches support changing of the load balancing algorithm, so if you fall into the single server-to-server category, make sure you allow it to round-robin the Ethernet frames.

Alternatively, you don't need to burn the expensive switch ports at all. Both servers can be connected together via crossover cables to the bonded interfaces. In this configuration, you want to use balance-rr mode on both sides, which we will explain momentarily.

Generic Bonding

There are multiple modes you can set in Linux, and the most common "generic" one is bonding-alb. This mode works effectively in most situations, without needing to configure a switch or trick anything else. It does, however, require that your network interface support changing the MAC address on the fly. This mode works well "generically" because it is constantly swapping MAC addresses to trick the other end (be it a switch or another connected host) into sending traffic across both links. This can wreak havoc on a Cisco network with port security enabled, but in general it's a quick and dirty way to get it working.

Channel Bonding Modes

Channel Bonding modes can be broken into three categories: generic, those that require switch support, and failover-only.

The failover-only mode is active-backup: One port is active until the link fails, then the other takes over the MAC and becomes active.

Modes that require switch support are:

  • balance-rr: Frames are transmitted in a round-robin fashion without hashing, to truly load balance.
  • 802.3ad: This mode is the official standard for link aggregation, and includes many configurable options for how to balance the traffic.
  • balance-xor: Traffic is hashed and balanced according to the receiver on the other end. This mode is also available as part of 802.3ad.

Note that modes requiring switch support can be run back-to-back with crossover cables between two server as well. This is especially useful, for example, when using DRBD to replicate two partitions.

Generic modes include:

  • broadcast: This mode is not really link aggregation - it simply broadcasts all traffic out both interfaces, which can be useful when sending data to partitioned broadcast domains for high availability (see below). If using broadcast mode on a single network, switch support is recommended.
  • balance-tlb: Outgoing traffic is load balanced, but incoming only uses a single interface. The driver will change the MAC address on the NIC when sending, but incoming always remains the same.
  • balance-alb: Both sending and receiving frames are load balanced using the change MAC address trick.

High Availability

How often have you seen a network die catastrophically? So bad that the link died? Chances are: never. More often you will see packet loss and very strange behavior. The failover part of NIC bonding is quite attractive to many administrators, but it rarely ever works. When the switch that both ports is connected to reboots for a firmware upgrade, you are down.

The easy fix is to connect each port to two distinct switches, right? If you are using a bonding mode that doesn't require switch support this will work fine. If, however, you are using a mode that requires switch support, this is not possible on most devices. Switches that support stacking, and are managed from a single point, often support EtherChannel across multiple switches. Ideally, you would would connect one port to each, and never reboot the whole stack of switches simultaneously.

Decisions

Bonding is simple once you understand the limitations of each mode. if you're working in an environment where switches support 802.3ad and you have no special needs, use that mode. Conversely, if you have no switch support and just want to increase throughput and enable failover, use balance-alb. Finally, if you just need a data replication link between two servers, balance-rr is the way to go.

----------------------------------------------------------------

 

Bonding (Port Trunking)

 

What is bonding?
Bonding is the same as port trunking. In the following I will use the word bonding because practically we will bond interfaces as one.

But still...what is bonding?
Bonding allows you to aggregate multiple ports into a single group, effectively combining the bandwidth into a single connection.  Bonding also allows you to create multi-gigabit pipes to transport traffic through the highest traffic areas of your network. For example, you can aggregate three megabits ports (1 mb each) into a three-megabits trunk port. That is equivalent with having one interface with three megabits speed.

Where should I use bonding?
You can use it wherever you need redundant links, fault tolerance or load balancing networks. It  is the best way to have a high availability network segment. A very useful way to use  bonding is to use it in connection with 802.1q VLAN support (your network equipment must have 802.1q  protocol implemented).

The best documentation is on the Linux Channel Bonding Project page
I strongly recommend to read it for more details.

Credits: Linux Channel Bonding Project page, Thea

This small howto will try to cover the most used bonding types. The following script (the gray area) will configure a bond interface (bond0)  using two ethernet interface (eth0 and eth1). You can place it onto your on file and run it  at boot time..

#!/bin/bash

modprobe bonding mode=0 miimon=100 # load bonding module

ifconfig eth0 down	# putting down the eth0 interface
ifconfig eth1 down	# putting down the eth1 interface

ifconfig bond0 hw ether 00:11:22:33:44:55	# changing the MAC address of the bond0 interface
ifconfig bond0 192.168.55.55 up	# to set ethX interfaces as slave the bond0 must have an ip.

ifenslave bond0 eth0	# putting the eth0 interface in the slave mod for bond0
ifenslave bond0 eth1	# putting the eth1 interface in the slave mod for bond0

You can set up your bond interface according to your needs. Changing one parameters  (mode=X) you can have the following bonding types:

mode=0 (balance-rr)
Round-robin policy: Transmit packets in sequential order from the first available slave  through the last.  This mode provides load balancing and fault tolerance.

mode=1 (active-backup)
Active-backup policy: Only one slave in the bond is active. A different slave becomes  active if, and only if, the active slave fails. The bond's MAC address is externally  visible on only one port (network adapter) to avoid confusing the switch.  This mode  provides fault tolerance. The primary option affects the behavior of this mode.

mode=2 (balance-xor)
XOR policy: Transmit based on [(source MAC address XOR'd with destination MAC address)  modulo slave count].  This selects the same slave for each destination MAC address. This  mode provides load balancing and fault tolerance.

mode=3 (broadcast)
Broadcast policy: transmits everything on all slave interfaces. This mode provides fault  tolerance.

mode=4 (802.3ad)
IEEE 802.3ad Dynamic link aggregation. Creates aggregation groups that share the same  speed and duplex settings.  Utilizes all slaves in the active aggregator according to  the 802.3ad specification.

	Pre-requisites:
	1. Ethtool support in the base drivers for retrieving
	the speed and duplex of each slave.
	2. A switch that supports IEEE 802.3ad Dynamic link
	aggregation.
	Most switches will require some type of configuration
	to enable 802.3ad mode.

mode=5 (balance-tlb)
Adaptive transmit load balancing: channel bonding that does not require any special  switch support. The outgoing traffic is distributed according to the current load  (computed relative to the speed) on each slave.  Incoming traffic is received by  the current slave.  If the receiving slave fails, another slave takes over the  MAC address of the failed receiving slave.

	Prerequisite:
	Ethtool support in the base drivers for retrieving the
	speed of each slave.

mode=6 (balance-alb)
Adaptive load balancing: includes balance-tlb plus receive load balancing (rlb) for  IPV4 traffic, and does not require any special switch support. The receive load  balancing is achieved by ARP negotiation. The bonding driver intercepts the ARP  Replies sent by the local system on their way out and overwrites the source hardware  address with the unique hardware address of one of the slaves in the bond  such that different peers use different hardware addresses for the server.

The most used are the first four mode types...

Also you can use multiple bond interface but for that you must load the bonding  module as many as you need.
Presuming that you want two bond interface you must configure the /etc/modules.conf  as follow:

	alias bond0 bonding
	options bond0 -o bond0 mode=0 miimon=100
	alias bond1 bonding
	options bond1 -o bond1 mode=1 miimon=100

Notes:

  • To restore your slaves MAC addresses, you need to detach them from the  bond (`ifenslave -d bond0 eth0'). The bonding driver will then restore the MAC  addresses that the slaves had before they were enslaved.
  • The bond MAC address will be the taken from its first slave device.
  • Promiscous mode: According to your bond type, when you put the bond interface in the promiscous  mode it will propogates the setting to the slave devices as follow:
    • for mode=0,2,3 and 4 the promiscuous mode setting is propogated to all slaves.
    • for mode=1,5 and 6 the promiscuous mode setting is propogated only to the active slave.
      For balance-tlb mode the active slave is the slave currently receiving inbound traffic, for balance-alb mode the active slave is the slave used as a "primary." and for the active-backup, balance-tlb and balance-alb modes, when the active slave  changes (e.g., due to a link failure), the promiscuous setting will be propogated to the new active slave.
    • ----------------------------------------------
    • Linux Network bonding – setup guide

      Linux network Bonding is creation of a single bonded interface by combining 2 or more Ethernet interfaces. This helps in high availability of your network interface and offers performance improvement. Bonding is same as port trunking or teaming.


      Bonding allows you to aggregate multiple ports into a single group, effectively combining the bandwidth into a single connection. Bonding also allows you to create multi-gigabit pipes to transport traffic through the highest traffic areas of your network. For example, you can aggregate three megabits ports into a three-megabits trunk port. That is equivalent with having one interface with three megabytes speed      

      Steps for bonding in Oracle Enterprise Linux and Redhat Enterprise Linux are as follows..      

      Step 1.

      Create the file ifcfg-bond0 with the IP address, netmask and gateway. Shown below is my test bonding config file.      

      $ cat /etc/sysconfig/network-scripts/ifcfg-bond0       

      DEVICE=bond0        
      IPADDR=192.168.1.12        
      NETMASK=255.255.255.0        
      GATEWAY=192.168.1.1        
      USERCTL=no        
      BOOTPROTO=none        
      ONBOOT=yes        

      Step 2.       

      Modify eth0, eth1 and eth2 configuration as shown below. Comment out, or remove the ip address, netmask, gateway and hardware address from each one of these files, since settings should only come from the ifcfg-bond0 file above. Make sure you add the MASTER and SLAVE configuration in these files.      

      $ cat /etc/sysconfig/network-scripts/ifcfg-eth0       

      DEVICE=eth0        
      BOOTPROTO=none        
      ONBOOT=yes        
      # Settings for Bond        
      MASTER=bond0        
      SLAVE=yes        

      $ cat /etc/sysconfig/network-scripts/ifcfg-eth1        

      DEVICE=eth1        
      BOOTPROTO=none 
      ONBOOT=yes        
      USERCTL=no        
      # Settings for bonding        
      MASTER=bond0        
      SLAVE=yes        

      $ cat /etc/sysconfig/network-scripts/ifcfg-eth2        

      DEVICE=eth2        
      BOOTPROTO=none        
      ONBOOT=yes        
      MASTER=bond0        
      SLAVE=yes


      Step 3.       

      Set the parameters for bond0 bonding kernel module. Select the network bonding mode based on you need, documented at http://unixfoo.blogspot.com/2008/02/network-bonding-part-ii-modes-of.html. The modes are

      • mode=0 (Balance Round Robin)
      • mode=1 (Active backup)
      • mode=2 (Balance XOR)
      • mode=3 (Broadcast)
      • mode=4 (802.3ad)
      • mode=5 (Balance TLB)
      • mode=6 (Balance ALB)

      Add the following lines to /etc/modprobe.conf

      # bonding commands           
      alias bond0 bonding            
      options bond0 mode=1 miimon=100            

      Step 4.

      Load the bond driver module from the command prompt.          

      $ modprobe bonding

      Step 5.

      Restart the network, or restart the computer.          

      $ service network restart # Or restart computer          

      When the machine boots up check the proc settings.          

      $ cat /proc/net/bonding/bond0           
      Ethernet Channel Bonding Driver: v3.0.2 (March 23, 2006)            

      Bonding Mode: adaptive load balancing            
      Primary Slave: None            
      Currently Active Slave: eth2            
      MII Status: up            
      MII Polling Interval (ms): 100            
      Up Delay (ms): 0            
      Down Delay (ms): 0            

      Slave Interface: eth2            
      MII Status: up            
      Link Failure Count: 0            
      Permanent HW addr: 00:13:72:80: 62:f0


      Look at ifconfig -a and check that your bond0 interface is active. You are done!. For more details on the different modes of bonding, please refer tounixfoo’s modes of bonding.         

      To verify whether the failover bonding works..

       

      • Do an ifdown eth0 and check /proc/net/bonding/bond0 and check the “Current Active slave”.
      • Do a continuous ping to the bond0 ipaddress from a different machine and do a ifdown the active interface. The ping should not break
      -----------------------------------------------------------


      		Linux Ethernet Bonding Driver HOWTO
      
      		Latest update: 27 April 2011
      
      Initial release : Thomas Davis 
      Corrections, HA extensions : 2000/10/03-15 :
        - Willy Tarreau 
        - Constantine Gavrilov 
        - Chad N. Tindel 
        - Janice Girouard 
        - Jay Vosburgh 
      
      Reorganized and updated Feb 2005 by Jay Vosburgh
      Added Sysfs information: 2006/04/24
        - Mitch Williams 
      
      Introduction
      ============
      
      	The Linux bonding driver provides a method for aggregating
      multiple network interfaces into a single logical "bonded" interface.
      The behavior of the bonded interfaces depends upon the mode; generally
      speaking, modes provide either hot standby or load balancing services.
      Additionally, link integrity monitoring may be performed.
      	
      	The bonding driver originally came from Donald Becker's
      beowulf patches for kernel 2.0. It has changed quite a bit since, and
      the original tools from extreme-linux and beowulf sites will not work
      with this version of the driver.
      
      	For new versions of the driver, updated userspace tools, and
      who to ask for help, please follow the links at the end of this file.
      
      Table of Contents
      =================
      
      1. Bonding Driver Installation
      
      2. Bonding Driver Options
      
      3. Configuring Bonding Devices
      3.1	Configuration with Sysconfig Support
      3.1.1		Using DHCP with Sysconfig
      3.1.2		Configuring Multiple Bonds with Sysconfig
      3.2	Configuration with Initscripts Support
      3.2.1		Using DHCP with Initscripts
      3.2.2		Configuring Multiple Bonds with Initscripts
      3.3	Configuring Bonding Manually with Ifenslave
      3.3.1		Configuring Multiple Bonds Manually
      3.4	Configuring Bonding Manually via Sysfs
      3.5	Configuration with Interfaces Support
      3.6	Overriding Configuration for Special Cases
      
      4. Querying Bonding Configuration
      4.1	Bonding Configuration
      4.2	Network Configuration
      
      5. Switch Configuration
      
      6. 802.1q VLAN Support
      
      7. Link Monitoring
      7.1	ARP Monitor Operation
      7.2	Configuring Multiple ARP Targets
      7.3	MII Monitor Operation
      
      8. Potential Trouble Sources
      8.1	Adventures in Routing
      8.2	Ethernet Device Renaming
      8.3	Painfully Slow Or No Failed Link Detection By Miimon
      
      9. SNMP agents
      
      10. Promiscuous mode
      
      11. Configuring Bonding for High Availability
      11.1	High Availability in a Single Switch Topology
      11.2	High Availability in a Multiple Switch Topology
      11.2.1		HA Bonding Mode Selection for Multiple Switch Topology
      11.2.2		HA Link Monitoring for Multiple Switch Topology
      
      12. Configuring Bonding for Maximum Throughput
      12.1	Maximum Throughput in a Single Switch Topology
      12.1.1		MT Bonding Mode Selection for Single Switch Topology
      12.1.2		MT Link Monitoring for Single Switch Topology
      12.2	Maximum Throughput in a Multiple Switch Topology
      12.2.1		MT Bonding Mode Selection for Multiple Switch Topology
      12.2.2		MT Link Monitoring for Multiple Switch Topology
      
      13. Switch Behavior Issues
      13.1	Link Establishment and Failover Delays
      13.2	Duplicated Incoming Packets
      
      14. Hardware Specific Considerations
      14.1	IBM BladeCenter
      
      15. Frequently Asked Questions
      
      16. Resources and Links
      
      
      1. Bonding Driver Installation
      ==============================
      
      	Most popular distro kernels ship with the bonding driver
      already available as a module and the ifenslave user level control
      program installed and ready for use. If your distro does not, or you
      have need to compile bonding from source (e.g., configuring and
      installing a mainline kernel from kernel.org), you'll need to perform
      the following steps:
      
      1.1 Configure and build the kernel with bonding
      -----------------------------------------------
      
      	The current version of the bonding driver is available in the
      drivers/net/bonding subdirectory of the most recent kernel source
      (which is available on http://kernel.org).  Most users "rolling their
      own" will want to use the most recent kernel from kernel.org.
      
      	Configure kernel with "make menuconfig" (or "make xconfig" or
      "make config"), then select "Bonding driver support" in the "Network
      device support" section.  It is recommended that you configure the
      driver as module since it is currently the only way to pass parameters
      to the driver or configure more than one bonding device.
      
      	Build and install the new kernel and modules, then continue
      below to install ifenslave.
      
      1.2 Install ifenslave Control Utility
      -------------------------------------
      
      	The ifenslave user level control program is included in the
      kernel source tree, in the file Documentation/networking/ifenslave.c.
      It is generally recommended that you use the ifenslave that
      corresponds to the kernel that you are using (either from the same
      source tree or supplied with the distro), however, ifenslave
      executables from older kernels should function (but features newer
      than the ifenslave release are not supported).  Running an ifenslave
      that is newer than the kernel is not supported, and may or may not
      work.
      
      	To install ifenslave, do the following:
      
      # gcc -Wall -O -I/usr/src/linux/include ifenslave.c -o ifenslave
      # cp ifenslave /sbin/ifenslave
      
      	If your kernel source is not in "/usr/src/linux," then replace
      "/usr/src/linux/include" in the above with the location of your kernel
      source include directory.
      
      	You may wish to back up any existing /sbin/ifenslave, or, for
      testing or informal use, tag the ifenslave to the kernel version
      (e.g., name the ifenslave executable /sbin/ifenslave-2.6.10).
      
      IMPORTANT NOTE:
      
      	If you omit the "-I" or specify an incorrect directory, you
      may end up with an ifenslave that is incompatible with the kernel
      you're trying to build it for.  Some distros (e.g., Red Hat from 7.1
      onwards) do not have /usr/include/linux symbolically linked to the
      default kernel source include directory.
      
      SECOND IMPORTANT NOTE:
      	If you plan to configure bonding using sysfs or using the
      /etc/network/interfaces file, you do not need to use ifenslave.
      
      2. Bonding Driver Options
      =========================
      
      	Options for the bonding driver are supplied as parameters to the
      bonding module at load time, or are specified via sysfs.
      
      	Module options may be given as command line arguments to the
      insmod or modprobe command, but are usually specified in either the
      /etc/modules.conf or /etc/modprobe.conf configuration file, or in a
      distro-specific configuration file (some of which are detailed in the next
      section).
      
      	Details on bonding support for sysfs is provided in the
      "Configuring Bonding Manually via Sysfs" section, below.
      
      	The available bonding driver parameters are listed below. If a
      parameter is not specified the default value is used.  When initially
      configuring a bond, it is recommended "tail -f /var/log/messages" be
      run in a separate window to watch for bonding driver error messages.
      
      	It is critical that either the miimon or arp_interval and
      arp_ip_target parameters be specified, otherwise serious network
      degradation will occur during link failures.  Very few devices do not
      support at least miimon, so there is really no reason not to use it.
      
      	Options with textual values will accept either the text name
      or, for backwards compatibility, the option value.  E.g.,
      "mode=802.3ad" and "mode=4" set the same mode.
      
      	The parameters are as follows:
      
      ad_select
      
      	Specifies the 802.3ad aggregation selection logic to use.  The
      	possible values and their effects are:
      
      	stable or 0
      
      		The active aggregator is chosen by largest aggregate
      		bandwidth.
      
      		Reselection of the active aggregator occurs only when all
      		slaves of the active aggregator are down or the active
      		aggregator has no slaves.
      
      		This is the default value.
      
      	bandwidth or 1
      
      		The active aggregator is chosen by largest aggregate
      		bandwidth.  Reselection occurs if:
      
      		- A slave is added to or removed from the bond
      
      		- Any slave's link state changes
      
      		- Any slave's 802.3ad association state changes
      
      		- The bond's administrative state changes to up
      
      	count or 2
      
      		The active aggregator is chosen by the largest number of
      		ports (slaves).  Reselection occurs as described under the
      		"bandwidth" setting, above.
      
      	The bandwidth and count selection policies permit failover of
      	802.3ad aggregations when partial failure of the active aggregator
      	occurs.  This keeps the aggregator with the highest availability
      	(either in bandwidth or in number of ports) active at all times.
      
      	This option was added in bonding version 3.4.0.
      
      arp_interval
      
      	Specifies the ARP link monitoring frequency in milliseconds.
      
      	The ARP monitor works by periodically checking the slave
      	devices to determine whether they have sent or received
      	traffic recently (the precise criteria depends upon the
      	bonding mode, and the state of the slave).  Regular traffic is
      	generated via ARP probes issued for the addresses specified by
      	the arp_ip_target option.
      
      	This behavior can be modified by the arp_validate option,
      	below.
      
      	If ARP monitoring is used in an etherchannel compatible mode
      	(modes 0 and 2), the switch should be configured in a mode
      	that evenly distributes packets across all links. If the
      	switch is configured to distribute the packets in an XOR
      	fashion, all replies from the ARP targets will be received on
      	the same link which could cause the other team members to
      	fail.  ARP monitoring should not be used in conjunction with
      	miimon.  A value of 0 disables ARP monitoring.  The default
      	value is 0.
      
      arp_ip_target
      
      	Specifies the IP addresses to use as ARP monitoring peers when
      	arp_interval is > 0.  These are the targets of the ARP request
      	sent to determine the health of the link to the targets.
      	Specify these values in ddd.ddd.ddd.ddd format.  Multiple IP
      	addresses must be separated by a comma.  At least one IP
      	address must be given for ARP monitoring to function.  The
      	maximum number of targets that can be specified is 16.  The
      	default value is no IP addresses.
      
      arp_validate
      
      	Specifies whether or not ARP probes and replies should be
      	validated in the active-backup mode.  This causes the ARP
      	monitor to examine the incoming ARP requests and replies, and
      	only consider a slave to be up if it is receiving the
      	appropriate ARP traffic.
      
      	Possible values are:
      
      	none or 0
      
      		No validation is performed.  This is the default.
      
      	active or 1
      
      		Validation is performed only for the active slave.
      
      	backup or 2
      
      		Validation is performed only for backup slaves.
      
      	all or 3
      
      		Validation is performed for all slaves.
      
      	For the active slave, the validation checks ARP replies to
      	confirm that they were generated by an arp_ip_target.  Since
      	backup slaves do not typically receive these replies, the
      	validation performed for backup slaves is on the ARP request
      	sent out via the active slave.  It is possible that some
      	switch or network configurations may result in situations
      	wherein the backup slaves do not receive the ARP requests; in
      	such a situation, validation of backup slaves must be
      	disabled.
      
      	This option is useful in network configurations in which
      	multiple bonding hosts are concurrently issuing ARPs to one or
      	more targets beyond a common switch.  Should the link between
      	the switch and target fail (but not the switch itself), the
      	probe traffic generated by the multiple bonding instances will
      	fool the standard ARP monitor into considering the links as
      	still up.  Use of the arp_validate option can resolve this, as
      	the ARP monitor will only consider ARP requests and replies
      	associated with its own instance of bonding.
      
      	This option was added in bonding version 3.1.0.
      
      downdelay
      
      	Specifies the time, in milliseconds, to wait before disabling
      	a slave after a link failure has been detected.  This option
      	is only valid for the miimon link monitor.  The downdelay
      	value should be a multiple of the miimon value; if not, it
      	will be rounded down to the nearest multiple.  The default
      	value is 0.
      
      fail_over_mac
      
      	Specifies whether active-backup mode should set all slaves to
      	the same MAC address at enslavement (the traditional
      	behavior), or, when enabled, perform special handling of the
      	bond's MAC address in accordance with the selected policy.
      
      	Possible values are:
      
      	none or 0
      
      		This setting disables fail_over_mac, and causes
      		bonding to set all slaves of an active-backup bond to
      		the same MAC address at enslavement time.  This is the
      		default.
      
      	active or 1
      
      		The "active" fail_over_mac policy indicates that the
      		MAC address of the bond should always be the MAC
      		address of the currently active slave.  The MAC
      		address of the slaves is not changed; instead, the MAC
      		address of the bond changes during a failover.
      
      		This policy is useful for devices that cannot ever
      		alter their MAC address, or for devices that refuse
      		incoming broadcasts with their own source MAC (which
      		interferes with the ARP monitor).
      
      		The down side of this policy is that every device on
      		the network must be updated via gratuitous ARP,
      		vs. just updating a switch or set of switches (which
      		often takes place for any traffic, not just ARP
      		traffic, if the switch snoops incoming traffic to
      		update its tables) for the traditional method.  If the
      		gratuitous ARP is lost, communication may be
      		disrupted.
      
      		When this policy is used in conjunction with the mii
      		monitor, devices which assert link up prior to being
      		able to actually transmit and receive are particularly
      		susceptible to loss of the gratuitous ARP, and an
      		appropriate updelay setting may be required.
      
      	follow or 2
      
      		The "follow" fail_over_mac policy causes the MAC
      		address of the bond to be selected normally (normally
      		the MAC address of the first slave added to the bond).
      		However, the second and subsequent slaves are not set
      		to this MAC address while they are in a backup role; a
      		slave is programmed with the bond's MAC address at
      		failover time (and the formerly active slave receives
      		the newly active slave's MAC address).
      
      		This policy is useful for multiport devices that
      		either become confused or incur a performance penalty
      		when multiple ports are programmed with the same MAC
      		address.
      
      
      	The default policy is none, unless the first slave cannot
      	change its MAC address, in which case the active policy is
      	selected by default.
      
      	This option may be modified via sysfs only when no slaves are
      	present in the bond.
      
      	This option was added in bonding version 3.2.0.  The "follow"
      	policy was added in bonding version 3.3.0.
      
      lacp_rate
      
      	Option specifying the rate in which we'll ask our link partner
      	to transmit LACPDU packets in 802.3ad mode.  Possible values
      	are:
      
      	slow or 0
      		Request partner to transmit LACPDUs every 30 seconds
      
      	fast or 1
      		Request partner to transmit LACPDUs every 1 second
      
      	The default is slow.
      
      max_bonds
      
      	Specifies the number of bonding devices to create for this
      	instance of the bonding driver.  E.g., if max_bonds is 3, and
      	the bonding driver is not already loaded, then bond0, bond1
      	and bond2 will be created.  The default value is 1.  Specifying
      	a value of 0 will load bonding, but will not create any devices.
      
      miimon
      
      	Specifies the MII link monitoring frequency in milliseconds.
      	This determines how often the link state of each slave is
      	inspected for link failures.  A value of zero disables MII
      	link monitoring.  A value of 100 is a good starting point.
      	The use_carrier option, below, affects how the link state is
      	determined.  See the High Availability section for additional
      	information.  The default value is 0.
      
      mode
      
      	Specifies one of the bonding policies. The default is
      	balance-rr (round robin).  Possible values are:
      
      	balance-rr or 0
      
      		Round-robin policy: Transmit packets in sequential
      		order from the first available slave through the
      		last.  This mode provides load balancing and fault
      		tolerance.
      
      	active-backup or 1
      
      		Active-backup policy: Only one slave in the bond is
      		active.  A different slave becomes active if, and only
      		if, the active slave fails.  The bond's MAC address is
      		externally visible on only one port (network adapter)
      		to avoid confusing the switch.
      
      		In bonding version 2.6.2 or later, when a failover
      		occurs in active-backup mode, bonding will issue one
      		or more gratuitous ARPs on the newly active slave.
      		One gratuitous ARP is issued for the bonding master
      		interface and each VLAN interfaces configured above
      		it, provided that the interface has at least one IP
      		address configured.  Gratuitous ARPs issued for VLAN
      		interfaces are tagged with the appropriate VLAN id.
      
      		This mode provides fault tolerance.  The primary
      		option, documented below, affects the behavior of this
      		mode.
      
      	balance-xor or 2
      
      		XOR policy: Transmit based on the selected transmit
      		hash policy.  The default policy is a simple [(source
      		MAC address XOR'd with destination MAC address) modulo
      		slave count].  Alternate transmit policies may be
      		selected via the xmit_hash_policy option, described
      		below.
      
      		This mode provides load balancing and fault tolerance.
      
      	broadcast or 3
      
      		Broadcast policy: transmits everything on all slave
      		interfaces.  This mode provides fault tolerance.
      
      	802.3ad or 4
      
      		IEEE 802.3ad Dynamic link aggregation.  Creates
      		aggregation groups that share the same speed and
      		duplex settings.  Utilizes all slaves in the active
      		aggregator according to the 802.3ad specification.
      
      		Slave selection for outgoing traffic is done according
      		to the transmit hash policy, which may be changed from
      		the default simple XOR policy via the xmit_hash_policy
      		option, documented below.  Note that not all transmit
      		policies may be 802.3ad compliant, particularly in
      		regards to the packet mis-ordering requirements of
      		section 43.2.4 of the 802.3ad standard.  Differing
      		peer implementations will have varying tolerances for
      		noncompliance.
      
      		Prerequisites:
      
      		1. Ethtool support in the base drivers for retrieving
      		the speed and duplex of each slave.
      
      		2. A switch that supports IEEE 802.3ad Dynamic link
      		aggregation.
      
      		Most switches will require some type of configuration
      		to enable 802.3ad mode.
      
      	balance-tlb or 5
      
      		Adaptive transmit load balancing: channel bonding that
      		does not require any special switch support.  The
      		outgoing traffic is distributed according to the
      		current load (computed relative to the speed) on each
      		slave.  Incoming traffic is received by the current
      		slave.  If the receiving slave fails, another slave
      		takes over the MAC address of the failed receiving
      		slave.
      
      		Prerequisite:
      
      		Ethtool support in the base drivers for retrieving the
      		speed of each slave.
      
      	balance-alb or 6
      
      		Adaptive load balancing: includes balance-tlb plus
      		receive load balancing (rlb) for IPV4 traffic, and
      		does not require any special switch support.  The
      		receive load balancing is achieved by ARP negotiation.
      		The bonding driver intercepts the ARP Replies sent by
      		the local system on their way out and overwrites the
      		source hardware address with the unique hardware
      		address of one of the slaves in the bond such that
      		different peers use different hardware addresses for
      		the server.
      
      		Receive traffic from connections created by the server
      		is also balanced.  When the local system sends an ARP
      		Request the bonding driver copies and saves the peer's
      		IP information from the ARP packet.  When the ARP
      		Reply arrives from the peer, its hardware address is
      		retrieved and the bonding driver initiates an ARP
      		reply to this peer assigning it to one of the slaves
      		in the bond.  A problematic outcome of using ARP
      		negotiation for balancing is that each time that an
      		ARP request is broadcast it uses the hardware address
      		of the bond.  Hence, peers learn the hardware address
      		of the bond and the balancing of receive traffic
      		collapses to the current slave.  This is handled by
      		sending updates (ARP Replies) to all the peers with
      		their individually assigned hardware address such that
      		the traffic is redistributed.  Receive traffic is also
      		redistributed when a new slave is added to the bond
      		and when an inactive slave is re-activated.  The
      		receive load is distributed sequentially (round robin)
      		among the group of highest speed slaves in the bond.
      
      		When a link is reconnected or a new slave joins the
      		bond the receive traffic is redistributed among all
      		active slaves in the bond by initiating ARP Replies
      		with the selected MAC address to each of the
      		clients. The updelay parameter (detailed below) must
      		be set to a value equal or greater than the switch's
      		forwarding delay so that the ARP Replies sent to the
      		peers will not be blocked by the switch.
      
      		Prerequisites:
      
      		1. Ethtool support in the base drivers for retrieving
      		the speed of each slave.
      
      		2. Base driver support for setting the hardware
      		address of a device while it is open.  This is
      		required so that there will always be one slave in the
      		team using the bond hardware address (the
      		curr_active_slave) while having a unique hardware
      		address for each slave in the bond.  If the
      		curr_active_slave fails its hardware address is
      		swapped with the new curr_active_slave that was
      		chosen.
      
      num_grat_arp
      num_unsol_na
      
      	Specify the number of peer notifications (gratuitous ARPs and
      	unsolicited IPv6 Neighbor Advertisements) to be issued after a
      	failover event.  As soon as the link is up on the new slave
      	(possibly immediately) a peer notification is sent on the
      	bonding device and each VLAN sub-device.  This is repeated at
      	each link monitor interval (arp_interval or miimon, whichever
      	is active) if the number is greater than 1.
      
      	The valid range is 0 - 255; the default value is 1.  These options
      	affect only the active-backup mode.  These options were added for
      	bonding versions 3.3.0 and 3.4.0 respectively.
      
      	From Linux 2.6.40 and bonding version 3.7.1, these notifications
      	are generated by the ipv4 and ipv6 code and the numbers of
      	repetitions cannot be set independently.
      
      primary
      
      	A string (eth0, eth2, etc) specifying which slave is the
      	primary device.  The specified device will always be the
      	active slave while it is available.  Only when the primary is
      	off-line will alternate devices be used.  This is useful when
      	one slave is preferred over another, e.g., when one slave has
      	higher throughput than another.
      
      	The primary option is only valid for active-backup mode.
      
      primary_reselect
      
      	Specifies the reselection policy for the primary slave.  This
      	affects how the primary slave is chosen to become the active slave
      	when failure of the active slave or recovery of the primary slave
      	occurs.  This option is designed to prevent flip-flopping between
      	the primary slave and other slaves.  Possible values are:
      
      	always or 0 (default)
      
      		The primary slave becomes the active slave whenever it
      		comes back up.
      
      	better or 1
      
      		The primary slave becomes the active slave when it comes
      		back up, if the speed and duplex of the primary slave is
      		better than the speed and duplex of the current active
      		slave.
      
      	failure or 2
      
      		The primary slave becomes the active slave only if the
      		current active slave fails and the primary slave is up.
      
      	The primary_reselect setting is ignored in two cases:
      
      		If no slaves are active, the first slave to recover is
      		made the active slave.
      
      		When initially enslaved, the primary slave is always made
      		the active slave.
      
      	Changing the primary_reselect policy via sysfs will cause an
      	immediate selection of the best active slave according to the new
      	policy.  This may or may not result in a change of the active
      	slave, depending upon the circumstances.
      
      	This option was added for bonding version 3.6.0.
      
      updelay
      
      	Specifies the time, in milliseconds, to wait before enabling a
      	slave after a link recovery has been detected.  This option is
      	only valid for the miimon link monitor.  The updelay value
      	should be a multiple of the miimon value; if not, it will be
      	rounded down to the nearest multiple.  The default value is 0.
      
      use_carrier
      
      	Specifies whether or not miimon should use MII or ETHTOOL
      	ioctls vs. netif_carrier_ok() to determine the link
      	status. The MII or ETHTOOL ioctls are less efficient and
      	utilize a deprecated calling sequence within the kernel.  The
      	netif_carrier_ok() relies on the device driver to maintain its
      	state with netif_carrier_on/off; at this writing, most, but
      	not all, device drivers support this facility.
      
      	If bonding insists that the link is up when it should not be,
      	it may be that your network device driver does not support
      	netif_carrier_on/off.  The default state for netif_carrier is
      	"carrier on," so if a driver does not support netif_carrier,
      	it will appear as if the link is always up.  In this case,
      	setting use_carrier to 0 will cause bonding to revert to the
      	MII / ETHTOOL ioctl method to determine the link state.
      
      	A value of 1 enables the use of netif_carrier_ok(), a value of
      	0 will use the deprecated MII / ETHTOOL ioctls.  The default
      	value is 1.
      
      xmit_hash_policy
      
      	Selects the transmit hash policy to use for slave selection in
      	balance-xor and 802.3ad modes.  Possible values are:
      
      	layer2
      
      		Uses XOR of hardware MAC addresses to generate the
      		hash.  The formula is
      
      		(source MAC XOR destination MAC) modulo slave count
      
      		This algorithm will place all traffic to a particular
      		network peer on the same slave.
      
      		This algorithm is 802.3ad compliant.
      
      	layer2+3
      
      		This policy uses a combination of layer2 and layer3
      		protocol information to generate the hash.
      
      		Uses XOR of hardware MAC addresses and IP addresses to
      		generate the hash.  The formula is
      
      		(((source IP XOR dest IP) AND 0xffff) XOR
      			( source MAC XOR destination MAC ))
      				modulo slave count
      
      		This algorithm will place all traffic to a particular
      		network peer on the same slave.  For non-IP traffic,
      		the formula is the same as for the layer2 transmit
      		hash policy.
      
      		This policy is intended to provide a more balanced
      		distribution of traffic than layer2 alone, especially
      		in environments where a layer3 gateway device is
      		required to reach most destinations.
      
      		This algorithm is 802.3ad compliant.
      
      	layer3+4
      
      		This policy uses upper layer protocol information,
      		when available, to generate the hash.  This allows for
      		traffic to a particular network peer to span multiple
      		slaves, although a single connection will not span
      		multiple slaves.
      
      		The formula for unfragmented TCP and UDP packets is
      
      		((source port XOR dest port) XOR
      			 ((source IP XOR dest IP) AND 0xffff)
      				modulo slave count
      
      		For fragmented TCP or UDP packets and all other IP
      		protocol traffic, the source and destination port
      		information is omitted.  For non-IP traffic, the
      		formula is the same as for the layer2 transmit hash
      		policy.
      
      		This policy is intended to mimic the behavior of
      		certain switches, notably Cisco switches with PFC2 as
      		well as some Foundry and IBM products.
      
      		This algorithm is not fully 802.3ad compliant.  A
      		single TCP or UDP conversation containing both
      		fragmented and unfragmented packets will see packets
      		striped across two interfaces.  This may result in out
      		of order delivery.  Most traffic types will not meet
      		this criteria, as TCP rarely fragments traffic, and
      		most UDP traffic is not involved in extended
      		conversations.  Other implementations of 802.3ad may
      		or may not tolerate this noncompliance.
      
      	The default value is layer2.  This option was added in bonding
      	version 2.6.3.  In earlier versions of bonding, this parameter
      	does not exist, and the layer2 policy is the only policy.  The
      	layer2+3 value was added for bonding version 3.2.2.
      
      resend_igmp
      
      	Specifies the number of IGMP membership reports to be issued after
      	a failover event. One membership report is issued immediately after
      	the failover, subsequent packets are sent in each 200ms interval.
      
      	The valid range is 0 - 255; the default value is 1. A value of 0
      	prevents the IGMP membership report from being issued in response
      	to the failover event.
      
      	This option is useful for bonding modes balance-rr (0), active-backup
      	(1), balance-tlb (5) and balance-alb (6), in which a failover can
      	switch the IGMP traffic from one slave to another.  Therefore a fresh
      	IGMP report must be issued to cause the switch to forward the incoming
      	IGMP traffic over the newly selected slave.
      
      	This option was added for bonding version 3.7.0.
      
      3. Configuring Bonding Devices
      ==============================
      
      	You can configure bonding using either your distro's network
      initialization scripts, or manually using either ifenslave or the
      sysfs interface.  Distros generally use one of three packages for the
      network initialization scripts: initscripts, sysconfig or interfaces.
      Recent versions of these packages have support for bonding, while older
      versions do not.
      
      	We will first describe the options for configuring bonding for
      distros using versions of initscripts, sysconfig and interfaces with full
      or partial support for bonding, then provide information on enabling
      bonding without support from the network initialization scripts (i.e.,
      older versions of initscripts or sysconfig).
      
      	If you're unsure whether your distro uses sysconfig,
      initscripts or interfaces, or don't know if it's new enough, have no fear.
      Determining this is fairly straightforward.
      
      	First, look for a file called interfaces in /etc/network directory.
      If this file is present in your system, then your system use interfaces. See
      Configuration with Interfaces Support.
      
      	Else, issue the command:
      
      $ rpm -qf /sbin/ifup
      
      	It will respond with a line of text starting with either
      "initscripts" or "sysconfig," followed by some numbers.  This is the
      package that provides your network initialization scripts.
      
      	Next, to determine if your installation supports bonding,
      issue the command:
      
      $ grep ifenslave /sbin/ifup
      
      	If this returns any matches, then your initscripts or
      sysconfig has support for bonding.
      
      3.1 Configuration with Sysconfig Support
      ----------------------------------------
      
      	This section applies to distros using a version of sysconfig
      with bonding support, for example, SuSE Linux Enterprise Server 9.
      
      	SuSE SLES 9's networking configuration system does support
      bonding, however, at this writing, the YaST system configuration
      front end does not provide any means to work with bonding devices.
      Bonding devices can be managed by hand, however, as follows.
      
      	First, if they have not already been configured, configure the
      slave devices.  On SLES 9, this is most easily done by running the
      yast2 sysconfig configuration utility.  The goal is for to create an
      ifcfg-id file for each slave device.  The simplest way to accomplish
      this is to configure the devices for DHCP (this is only to get the
      file ifcfg-id file created; see below for some issues with DHCP).  The
      name of the configuration file for each device will be of the form:
      
      ifcfg-id-xx:xx:xx:xx:xx:xx
      
      	Where the "xx" portion will be replaced with the digits from
      the device's permanent MAC address.
      
      	Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been
      created, it is necessary to edit the configuration files for the slave
      devices (the MAC addresses correspond to those of the slave devices).
      Before editing, the file will contain multiple lines, and will look
      something like this:
      
      BOOTPROTO='dhcp'
      STARTMODE='on'
      USERCTL='no'
      UNIQUE='XNzu.WeZGOGF+4wE'
      _nm_name='bus-pci-0001:61:01.0'
      
      	Change the BOOTPROTO and STARTMODE lines to the following:
      
      BOOTPROTO='none'
      STARTMODE='off'
      
      	Do not alter the UNIQUE or _nm_name lines.  Remove any other
      lines (USERCTL, etc).
      
      	Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified,
      it's time to create the configuration file for the bonding device
      itself.  This file is named ifcfg-bondX, where X is the number of the
      bonding device to create, starting at 0.  The first such file is
      ifcfg-bond0, the second is ifcfg-bond1, and so on.  The sysconfig
      network configuration system will correctly start multiple instances
      of bonding.
      
      	The contents of the ifcfg-bondX file is as follows:
      
      BOOTPROTO="static"
      BROADCAST="10.0.2.255"
      IPADDR="10.0.2.10"
      NETMASK="255.255.0.0"
      NETWORK="10.0.2.0"
      REMOTE_IPADDR=""
      STARTMODE="onboot"
      BONDING_MASTER="yes"
      BONDING_MODULE_OPTS="mode=active-backup miimon=100"
      BONDING_SLAVE0="eth0"
      BONDING_SLAVE1="bus-pci-0000:06:08.1"
      
      	Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK
      values with the appropriate values for your network.
      
      	The STARTMODE specifies when the device is brought online.
      The possible values are:
      
      	onboot:	 The device is started at boot time.  If you're not
      		 sure, this is probably what you want.
      
      	manual:	 The device is started only when ifup is called
      		 manually.  Bonding devices may be configured this
      		 way if you do not wish them to start automatically
      		 at boot for some reason.
      
      	hotplug: The device is started by a hotplug event.  This is not
      		 a valid choice for a bonding device.
      
      	off or ignore: The device configuration is ignored.
      
      	The line BONDING_MASTER='yes' indicates that the device is a
      bonding master device.  The only useful value is "yes."
      
      	The contents of BONDING_MODULE_OPTS are supplied to the
      instance of the bonding module for this device.  Specify the options
      for the bonding mode, link monitoring, and so on here.  Do not include
      the max_bonds bonding parameter; this will confuse the configuration
      system if you have multiple bonding devices.
      
      	Finally, supply one BONDING_SLAVEn="slave device" for each
      slave.  where "n" is an increasing value, one for each slave.  The
      "slave device" is either an interface name, e.g., "eth0", or a device
      specifier for the network device.  The interface name is easier to
      find, but the ethN names are subject to change at boot time if, e.g.,
      a device early in the sequence has failed.  The device specifiers
      (bus-pci-0000:06:08.1 in the example above) specify the physical
      network device, and will not change unless the device's bus location
      changes (for example, it is moved from one PCI slot to another).  The
      example above uses one of each type for demonstration purposes; most
      configurations will choose one or the other for all slave devices.
      
      	When all configuration files have been modified or created,
      networking must be restarted for the configuration changes to take
      effect.  This can be accomplished via the following:
      
      # /etc/init.d/network restart
      
      	Note that the network control script (/sbin/ifdown) will
      remove the bonding module as part of the network shutdown processing,
      so it is not necessary to remove the module by hand if, e.g., the
      module parameters have changed.
      
      	Also, at this writing, YaST/YaST2 will not manage bonding
      devices (they do not show bonding interfaces on its list of network
      devices).  It is necessary to edit the configuration file by hand to
      change the bonding configuration.
      
      	Additional general options and details of the ifcfg file
      format can be found in an example ifcfg template file:
      
      /etc/sysconfig/network/ifcfg.template
      
      	Note that the template does not document the various BONDING_
      settings described above, but does describe many of the other options.
      
      3.1.1 Using DHCP with Sysconfig
      -------------------------------
      
      	Under sysconfig, configuring a device with BOOTPROTO='dhcp'
      will cause it to query DHCP for its IP address information.  At this
      writing, this does not function for bonding devices; the scripts
      attempt to obtain the device address from DHCP prior to adding any of
      the slave devices.  Without active slaves, the DHCP requests are not
      sent to the network.
      
      3.1.2 Configuring Multiple Bonds with Sysconfig
      -----------------------------------------------
      
      	The sysconfig network initialization system is capable of
      handling multiple bonding devices.  All that is necessary is for each
      bonding instance to have an appropriately configured ifcfg-bondX file
      (as described above).  Do not specify the "max_bonds" parameter to any
      instance of bonding, as this will confuse sysconfig.  If you require
      multiple bonding devices with identical parameters, create multiple
      ifcfg-bondX files.
      
      	Because the sysconfig scripts supply the bonding module
      options in the ifcfg-bondX file, it is not necessary to add them to
      the system /etc/modules.conf or /etc/modprobe.conf configuration file.
      
      3.2 Configuration with Initscripts Support
      ------------------------------------------
      
      	This section applies to distros using a recent version of
      initscripts with bonding support, for example, Red Hat Enterprise Linux
      version 3 or later, Fedora, etc.  On these systems, the network
      initialization scripts have knowledge of bonding, and can be configured to
      control bonding devices.  Note that older versions of the initscripts
      package have lower levels of support for bonding; this will be noted where
      applicable.
      
      	These distros will not automatically load the network adapter
      driver unless the ethX device is configured with an IP address.
      Because of this constraint, users must manually configure a
      network-script file for all physical adapters that will be members of
      a bondX link.  Network script files are located in the directory:
      
      /etc/sysconfig/network-scripts
      
      	The file name must be prefixed with "ifcfg-eth" and suffixed
      with the adapter's physical adapter number.  For example, the script
      for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0.
      Place the following text in the file:
      
      DEVICE=eth0
      USERCTL=no
      ONBOOT=yes
      MASTER=bond0
      SLAVE=yes
      BOOTPROTO=none
      
      	The DEVICE= line will be different for every ethX device and
      must correspond with the name of the file, i.e., ifcfg-eth1 must have
      a device line of DEVICE=eth1.  The setting of the MASTER= line will
      also depend on the final bonding interface name chosen for your bond.
      As with other network devices, these typically start at 0, and go up
      one for each device, i.e., the first bonding instance is bond0, the
      second is bond1, and so on.
      
      	Next, create a bond network script.  The file name for this
      script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is
      the number of the bond.  For bond0 the file is named "ifcfg-bond0",
      for bond1 it is named "ifcfg-bond1", and so on.  Within that file,
      place the following text:
      
      DEVICE=bond0
      IPADDR=192.168.1.1
      NETMASK=255.255.255.0
      NETWORK=192.168.1.0
      BROADCAST=192.168.1.255
      ONBOOT=yes
      BOOTPROTO=none
      USERCTL=no
      
      	Be sure to change the networking specific lines (IPADDR,
      NETMASK, NETWORK and BROADCAST) to match your network configuration.
      
      	For later versions of initscripts, such as that found with Fedora
      7 (or later) and Red Hat Enterprise Linux version 5 (or later), it is possible,
      and, indeed, preferable, to specify the bonding options in the ifcfg-bond0
      file, e.g. a line of the format:
      
      BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target=192.168.1.254"
      
      	will configure the bond with the specified options.  The options
      specified in BONDING_OPTS are identical to the bonding module parameters
      except for the arp_ip_target field when using versions of initscripts older
      than and 8.57 (Fedora 8) and 8.45.19 (Red Hat Enterprise Linux 5.2).  When
      using older versions each target should be included as a separate option and
      should be preceded by a '+' to indicate it should be added to the list of
      queried targets, e.g.,
      
      	arp_ip_target=+192.168.1.1 arp_ip_target=+192.168.1.2
      
      	is the proper syntax to specify multiple targets.  When specifying
      options via BONDING_OPTS, it is not necessary to edit /etc/modules.conf or
      /etc/modprobe.conf.
      
      	For even older versions of initscripts that do not support
      BONDING_OPTS, it is necessary to edit /etc/modules.conf (or
      /etc/modprobe.conf, depending upon your distro) to load the bonding module
      with your desired options when the bond0 interface is brought up.  The
      following lines in /etc/modules.conf (or modprobe.conf) will load the
      bonding module, and select its options:
      
      alias bond0 bonding
      options bond0 mode=balance-alb miimon=100
      
      	Replace the sample parameters with the appropriate set of
      options for your configuration.
      
      	Finally run "/etc/rc.d/init.d/network restart" as root.  This
      will restart the networking subsystem and your bond link should be now
      up and running.
      
      3.2.1 Using DHCP with Initscripts
      ---------------------------------
      
      	Recent versions of initscripts (the versions supplied with Fedora
      Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to
      work) have support for assigning IP information to bonding devices via
      DHCP.
      
      	To configure bonding for DHCP, configure it as described
      above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp"
      and add a line consisting of "TYPE=Bonding".  Note that the TYPE value
      is case sensitive.
      
      3.2.2 Configuring Multiple Bonds with Initscripts
      -------------------------------------------------
      
      	Initscripts packages that are included with Fedora 7 and Red Hat
      Enterprise Linux 5 support multiple bonding interfaces by simply
      specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the
      number of the bond.  This support requires sysfs support in the kernel,
      and a bonding driver of version 3.0.0 or later.  Other configurations may
      not support this method for specifying multiple bonding interfaces; for
      those instances, see the "Configuring Multiple Bonds Manually" section,
      below.
      
      3.3 Configuring Bonding Manually with Ifenslave
      -----------------------------------------------
      
      	This section applies to distros whose network initialization
      scripts (the sysconfig or initscripts package) do not have specific
      knowledge of bonding.  One such distro is SuSE Linux Enterprise Server
      version 8.
      
      	The general method for these systems is to place the bonding
      module parameters into /etc/modules.conf or /etc/modprobe.conf (as
      appropriate for the installed distro), then add modprobe and/or
      ifenslave commands to the system's global init script.  The name of
      the global init script differs; for sysconfig, it is
      /etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local.
      
      	For example, if you wanted to make a simple bond of two e100
      devices (presumed to be eth0 and eth1), and have it persist across
      reboots, edit the appropriate file (/etc/init.d/boot.local or
      /etc/rc.d/rc.local), and add the following:
      
      modprobe bonding mode=balance-alb miimon=100
      modprobe e100
      ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
      ifenslave bond0 eth0
      ifenslave bond0 eth1
      
      	Replace the example bonding module parameters and bond0
      network configuration (IP address, netmask, etc) with the appropriate
      values for your configuration.
      
      	Unfortunately, this method will not provide support for the
      ifup and ifdown scripts on the bond devices.  To reload the bonding
      configuration, it is necessary to run the initialization script, e.g.,
      
      # /etc/init.d/boot.local
      
      	or
      
      # /etc/rc.d/rc.local
      
      	It may be desirable in such a case to create a separate script
      which only initializes the bonding configuration, then call that
      separate script from within boot.local.  This allows for bonding to be
      enabled without re-running the entire global init script.
      
      	To shut down the bonding devices, it is necessary to first
      mark the bonding device itself as being down, then remove the
      appropriate device driver modules.  For our example above, you can do
      the following:
      
      # ifconfig bond0 down
      # rmmod bonding
      # rmmod e100
      
      	Again, for convenience, it may be desirable to create a script
      with these commands.
      
      
      3.3.1 Configuring Multiple Bonds Manually
      -----------------------------------------
      
      	This section contains information on configuring multiple
      bonding devices with differing options for those systems whose network
      initialization scripts lack support for configuring multiple bonds.
      
      	If you require multiple bonding devices, but all with the same
      options, you may wish to use the "max_bonds" module parameter,
      documented above.
      
      	To create multiple bonding devices with differing options, it is
      preferrable to use bonding parameters exported by sysfs, documented in the
      section below.
      
      	For versions of bonding without sysfs support, the only means to
      provide multiple instances of bonding with differing options is to load
      the bonding driver multiple times.  Note that current versions of the
      sysconfig network initialization scripts handle this automatically; if
      your distro uses these scripts, no special action is needed.  See the
      section Configuring Bonding Devices, above, if you're not sure about your
      network initialization scripts.
      
      	To load multiple instances of the module, it is necessary to
      specify a different name for each instance (the module loading system
      requires that every loaded module, even multiple instances of the same
      module, have a unique name).  This is accomplished by supplying multiple
      sets of bonding options in /etc/modprobe.conf, for example:
      
      alias bond0 bonding
      options bond0 -o bond0 mode=balance-rr miimon=100
      
      alias bond1 bonding
      options bond1 -o bond1 mode=balance-alb miimon=50
      
      	will load the bonding module two times.  The first instance is
      named "bond0" and creates the bond0 device in balance-rr mode with an
      miimon of 100.  The second instance is named "bond1" and creates the
      bond1 device in balance-alb mode with an miimon of 50.
      
      	In some circumstances (typically with older distributions),
      the above does not work, and the second bonding instance never sees
      its options.  In that case, the second options line can be substituted
      as follows:
      
      install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
      	mode=balance-alb miimon=50
      
      	This may be repeated any number of times, specifying a new and
      unique name in place of bond1 for each subsequent instance.
      
      	It has been observed that some Red Hat supplied kernels are unable
      to rename modules at load time (the "-o bond1" part).  Attempts to pass
      that option to modprobe will produce an "Operation not permitted" error.
      This has been reported on some Fedora Core kernels, and has been seen on
      RHEL 4 as well.  On kernels exhibiting this problem, it will be impossible
      to configure multiple bonds with differing parameters (as they are older
      kernels, and also lack sysfs support).
      
      3.4 Configuring Bonding Manually via Sysfs
      ------------------------------------------
      
      	Starting with version 3.0.0, Channel Bonding may be configured
      via the sysfs interface.  This interface allows dynamic configuration
      of all bonds in the system without unloading the module.  It also
      allows for adding and removing bonds at runtime.  Ifenslave is no
      longer required, though it is still supported.
      
      	Use of the sysfs interface allows you to use multiple bonds
      with different configurations without having to reload the module.
      It also allows you to use multiple, differently configured bonds when
      bonding is compiled into the kernel.
      
      	You must have the sysfs filesystem mounted to configure
      bonding this way.  The examples in this document assume that you
      are using the standard mount point for sysfs, e.g. /sys.  If your
      sysfs filesystem is mounted elsewhere, you will need to adjust the
      example paths accordingly.
      
      Creating and Destroying Bonds
      -----------------------------
      To add a new bond foo:
      # echo +foo > /sys/class/net/bonding_masters
      
      To remove an existing bond bar:
      # echo -bar > /sys/class/net/bonding_masters
      
      To show all existing bonds:
      # cat /sys/class/net/bonding_masters
      
      NOTE: due to 4K size limitation of sysfs files, this list may be
      truncated if you have more than a few hundred bonds.  This is unlikely
      to occur under normal operating conditions.
      
      Adding and Removing Slaves
      --------------------------
      	Interfaces may be enslaved to a bond using the file
      /sys/class/net//bonding/slaves.  The semantics for this file
      are the same as for the bonding_masters file.
      
      To enslave interface eth0 to bond bond0:
      # ifconfig bond0 up
      # echo +eth0 > /sys/class/net/bond0/bonding/slaves
      
      To free slave eth0 from bond bond0:
      # echo -eth0 > /sys/class/net/bond0/bonding/slaves
      
      	When an interface is enslaved to a bond, symlinks between the
      two are created in the sysfs filesystem.  In this case, you would get
      /sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and
      /sys/class/net/eth0/master pointing to /sys/class/net/bond0.
      
      	This means that you can tell quickly whether or not an
      interface is enslaved by looking for the master symlink.  Thus:
      # echo -eth0 > /sys/class/net/eth0/master/bonding/slaves
      will free eth0 from whatever bond it is enslaved to, regardless of
      the name of the bond interface.
      
      Changing a Bond's Configuration
      -------------------------------
      	Each bond may be configured individually by manipulating the
      files located in /sys/class/net//bonding
      
      	The names of these files correspond directly with the command-
      line parameters described elsewhere in this file, and, with the
      exception of arp_ip_target, they accept the same values.  To see the
      current setting, simply cat the appropriate file.
      
      	A few examples will be given here; for specific usage
      guidelines for each parameter, see the appropriate section in this
      document.
      
      To configure bond0 for balance-alb mode:
      # ifconfig bond0 down
      # echo 6 > /sys/class/net/bond0/bonding/mode
       - or -
      # echo balance-alb > /sys/class/net/bond0/bonding/mode
      	NOTE: The bond interface must be down before the mode can be
      changed.
      
      To enable MII monitoring on bond0 with a 1 second interval:
      # echo 1000 > /sys/class/net/bond0/bonding/miimon
      	NOTE: If ARP monitoring is enabled, it will disabled when MII
      monitoring is enabled, and vice-versa.
      
      To add ARP targets:
      # echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
      # echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target
      	NOTE:  up to 16 target addresses may be specified.
      
      To remove an ARP target:
      # echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
      
      Example Configuration
      ---------------------
      	We begin with the same example that is shown in section 3.3,
      executed with sysfs, and without using ifenslave.
      
      	To make a simple bond of two e100 devices (presumed to be eth0
      and eth1), and have it persist across reboots, edit the appropriate
      file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the
      following:
      
      modprobe bonding
      modprobe e100
      echo balance-alb > /sys/class/net/bond0/bonding/mode
      ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
      echo 100 > /sys/class/net/bond0/bonding/miimon
      echo +eth0 > /sys/class/net/bond0/bonding/slaves
      echo +eth1 > /sys/class/net/bond0/bonding/slaves
      
      	To add a second bond, with two e1000 interfaces in
      active-backup mode, using ARP monitoring, add the following lines to
      your init script:
      
      modprobe e1000
      echo +bond1 > /sys/class/net/bonding_masters
      echo active-backup > /sys/class/net/bond1/bonding/mode
      ifconfig bond1 192.168.2.1 netmask 255.255.255.0 up
      echo +192.168.2.100 /sys/class/net/bond1/bonding/arp_ip_target
      echo 2000 > /sys/class/net/bond1/bonding/arp_interval
      echo +eth2 > /sys/class/net/bond1/bonding/slaves
      echo +eth3 > /sys/class/net/bond1/bonding/slaves
      
      3.5 Configuration with Interfaces Support
      -----------------------------------------
      
              This section applies to distros which use /etc/network/interfaces file
      to describe network interface configuration, most notably Debian and it's
      derivatives.
      
      	The ifup and ifdown commands on Debian don't support bonding out of
      the box. The ifenslave-2.6 package should be installed to provide bonding
      support.  Once installed, this package will provide bond-* options to be used
      into /etc/network/interfaces.
      
      	Note that ifenslave-2.6 package will load the bonding module and use
      the ifenslave command when appropriate.
      
      Example Configurations
      ----------------------
      
      In /etc/network/interfaces, the following stanza will configure bond0, in
      active-backup mode, with eth0 and eth1 as slaves.
      
      auto bond0
      iface bond0 inet dhcp
      	bond-slaves eth0 eth1
      	bond-mode active-backup
      	bond-miimon 100
      	bond-primary eth0 eth1
      
      If the above configuration doesn't work, you might have a system using
      upstart for system startup. This is most notably true for recent
      Ubuntu versions. The following stanza in /etc/network/interfaces will
      produce the same result on those systems.
      
      auto bond0
      iface bond0 inet dhcp
      	bond-slaves none
      	bond-mode active-backup
      	bond-miimon 100
      
      auto eth0
      iface eth0 inet manual
      	bond-master bond0
      	bond-primary eth0 eth1
      
      auto eth1
      iface eth1 inet manual
      	bond-master bond0
      	bond-primary eth0 eth1
      
      For a full list of bond-* supported options in /etc/network/interfaces and some
      more advanced examples tailored to you particular distros, see the files in
      /usr/share/doc/ifenslave-2.6.
      
      3.6 Overriding Configuration for Special Cases
      ----------------------------------------------
      
      When using the bonding driver, the physical port which transmits a frame is
      typically selected by the bonding driver, and is not relevant to the user or
      system administrator.  The output port is simply selected using the policies of
      the selected bonding mode.  On occasion however, it is helpful to direct certain
      classes of traffic to certain physical interfaces on output to implement
      slightly more complex policies.  For example, to reach a web server over a
      bonded interface in which eth0 connects to a private network, while eth1
      connects via a public network, it may be desirous to bias the bond to send said
      traffic over eth0 first, using eth1 only as a fall back, while all other traffic
      can safely be sent over either interface.  Such configurations may be achieved
      using the traffic control utilities inherent in linux.
      
      By default the bonding driver is multiqueue aware and 16 queues are created
      when the driver initializes (see Documentation/networking/multiqueue.txt
      for details).  If more or less queues are desired the module parameter
      tx_queues can be used to change this value.  There is no sysfs parameter
      available as the allocation is done at module init time.
      
      The output of the file /proc/net/bonding/bondX has changed so the output Queue
      ID is now printed for each slave:
      
      Bonding Mode: fault-tolerance (active-backup)
      Primary Slave: None
      Currently Active Slave: eth0
      MII Status: up
      MII Polling Interval (ms): 0
      Up Delay (ms): 0
      Down Delay (ms): 0
      
      Slave Interface: eth0
      MII Status: up
      Link Failure Count: 0
      Permanent HW addr: 00:1a:a0:12:8f:cb
      Slave queue ID: 0
      
      Slave Interface: eth1
      MII Status: up
      Link Failure Count: 0
      Permanent HW addr: 00:1a:a0:12:8f:cc
      Slave queue ID: 2
      
      The queue_id for a slave can be set using the command:
      
      # echo "eth1:2" > /sys/class/net/bond0/bonding/queue_id
      
      Any interface that needs a queue_id set should set it with multiple calls
      like the one above until proper priorities are set for all interfaces.  On
      distributions that allow configuration via initscripts, multiple 'queue_id'
      arguments can be added to BONDING_OPTS to set all needed slave queues.
      
      These queue id's can be used in conjunction with the tc utility to configure
      a multiqueue qdisc and filters to bias certain traffic to transmit on certain
      slave devices.  For instance, say we wanted, in the above configuration to
      force all traffic bound to 192.168.1.100 to use eth1 in the bond as its output
      device. The following commands would accomplish this:
      
      # tc qdisc add dev bond0 handle 1 root multiq
      
      # tc filter add dev bond0 protocol ip parent 1: prio 1 u32 match ip dst \
      	192.168.1.100 action skbedit queue_mapping 2
      
      These commands tell the kernel to attach a multiqueue queue discipline to the
      bond0 interface and filter traffic enqueued to it, such that packets with a dst
      ip of 192.168.1.100 have their output queue mapping value overwritten to 2.
      This value is then passed into the driver, causing the normal output path
      selection policy to be overridden, selecting instead qid 2, which maps to eth1.
      
      Note that qid values begin at 1.  Qid 0 is reserved to initiate to the driver
      that normal output policy selection should take place.  One benefit to simply
      leaving the qid for a slave to 0 is the multiqueue awareness in the bonding
      driver that is now present.  This awareness allows tc filters to be placed on
      slave devices as well as bond devices and the bonding driver will simply act as
      a pass-through for selecting output queues on the slave device rather than 
      output port selection.
      
      This feature first appeared in bonding driver version 3.7.0 and support for
      output slave selection was limited to round-robin and active-backup modes.
      
      4 Querying Bonding Configuration
      =================================
      
      4.1 Bonding Configuration
      -------------------------
      
      	Each bonding device has a read-only file residing in the
      /proc/net/bonding directory.  The file contents include information
      about the bonding configuration, options and state of each slave.
      
      	For example, the contents of /proc/net/bonding/bond0 after the
      driver is loaded with parameters of mode=0 and miimon=1000 is
      generally as follows:
      
      	Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004)
              Bonding Mode: load balancing (round-robin)
              Currently Active Slave: eth0
              MII Status: up
              MII Polling Interval (ms): 1000
              Up Delay (ms): 0
              Down Delay (ms): 0
      
              Slave Interface: eth1
              MII Status: up
              Link Failure Count: 1
      
              Slave Interface: eth0
              MII Status: up
              Link Failure Count: 1
      
      	The precise format and contents will change depending upon the
      bonding configuration, state, and version of the bonding driver.
      
      4.2 Network configuration
      -------------------------
      
      	The network configuration can be inspected using the ifconfig
      command.  Bonding devices will have the MASTER flag set; Bonding slave
      devices will have the SLAVE flag set.  The ifconfig output does not
      contain information on which slaves are associated with which masters.
      
      	In the example below, the bond0 interface is the master
      (MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of
      bond0 have the same MAC address (HWaddr) as bond0 for all modes except
      TLB and ALB that require a unique MAC address for each slave.
      
      # /sbin/ifconfig
      bond0     Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
                inet addr:XXX.XXX.XXX.YYY  Bcast:XXX.XXX.XXX.255  Mask:255.255.252.0
                UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1
                RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
                TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
                collisions:0 txqueuelen:0
      
      eth0      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
                UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
                RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
                TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
                collisions:0 txqueuelen:100
                Interrupt:10 Base address:0x1080
      
      eth1      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
                UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
                RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
                TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
                collisions:0 txqueuelen:100
                Interrupt:9 Base address:0x1400
      
      5. Switch Configuration
      =======================
      
      	For this section, "switch" refers to whatever system the
      bonded devices are directly connected to (i.e., where the other end of
      the cable plugs into).  This may be an actual dedicated switch device,
      or it may be another regular system (e.g., another computer running
      Linux),
      
      	The active-backup, balance-tlb and balance-alb modes do not
      require any specific configuration of the switch.
      
      	The 802.3ad mode requires that the switch have the appropriate
      ports configured as an 802.3ad aggregation.  The precise method used
      to configure this varies from switch to switch, but, for example, a
      Cisco 3550 series switch requires that the appropriate ports first be
      grouped together in a single etherchannel instance, then that
      etherchannel is set to mode "lacp" to enable 802.3ad (instead of
      standard EtherChannel).
      
      	The balance-rr, balance-xor and broadcast modes generally
      require that the switch have the appropriate ports grouped together.
      The nomenclature for such a group differs between switches, it may be
      called an "etherchannel" (as in the Cisco example, above), a "trunk
      group" or some other similar variation.  For these modes, each switch
      will also have its own configuration options for the switch's transmit
      policy to the bond.  Typical choices include XOR of either the MAC or
      IP addresses.  The transmit policy of the two peers does not need to
      match.  For these three modes, the bonding mode really selects a
      transmit policy for an EtherChannel group; all three will interoperate
      with another EtherChannel group.
      
      
      6. 802.1q VLAN Support
      ======================
      
      	It is possible to configure VLAN devices over a bond interface
      using the 8021q driver.  However, only packets coming from the 8021q
      driver and passing through bonding will be tagged by default.  Self
      generated packets, for example, bonding's learning packets or ARP
      packets generated by either ALB mode or the ARP monitor mechanism, are
      tagged internally by bonding itself.  As a result, bonding must
      "learn" the VLAN IDs configured above it, and use those IDs to tag
      self generated packets.
      
      	For reasons of simplicity, and to support the use of adapters
      that can do VLAN hardware acceleration offloading, the bonding
      interface declares itself as fully hardware offloading capable, it gets
      the add_vid/kill_vid notifications to gather the necessary
      information, and it propagates those actions to the slaves.  In case
      of mixed adapter types, hardware accelerated tagged packets that
      should go through an adapter that is not offloading capable are
      "un-accelerated" by the bonding driver so the VLAN tag sits in the
      regular location.
      
      	VLAN interfaces *must* be added on top of a bonding interface
      only after enslaving at least one slave.  The bonding interface has a
      hardware address of 00:00:00:00:00:00 until the first slave is added.
      If the VLAN interface is created prior to the first enslavement, it
      would pick up the all-zeroes hardware address.  Once the first slave
      is attached to the bond, the bond device itself will pick up the
      slave's hardware address, which is then available for the VLAN device.
      
      	Also, be aware that a similar problem can occur if all slaves
      are released from a bond that still has one or more VLAN interfaces on
      top of it.  When a new slave is added, the bonding interface will
      obtain its hardware address from the first slave, which might not
      match the hardware address of the VLAN interfaces (which was
      ultimately copied from an earlier slave).
      
      	There are two methods to insure that the VLAN device operates
      with the correct hardware address if all slaves are removed from a
      bond interface:
      
      	1. Remove all VLAN interfaces then recreate them
      
      	2. Set the bonding interface's hardware address so that it
      matches the hardware address of the VLAN interfaces.
      
      	Note that changing a VLAN interface's HW address would set the
      underlying device -- i.e. the bonding interface -- to promiscuous
      mode, which might not be what you want.
      
      
      7. Link Monitoring
      ==================
      
      	The bonding driver at present supports two schemes for
      monitoring a slave device's link state: the ARP monitor and the MII
      monitor.
      
      	At the present time, due to implementation restrictions in the
      bonding driver itself, it is not possible to enable both ARP and MII
      monitoring simultaneously.
      
      7.1 ARP Monitor Operation
      -------------------------
      
      	The ARP monitor operates as its name suggests: it sends ARP
      queries to one or more designated peer systems on the network, and
      uses the response as an indication that the link is operating.  This
      gives some assurance that traffic is actually flowing to and from one
      or more peers on the local network.
      
      	The ARP monitor relies on the device driver itself to verify
      that traffic is flowing.  In particular, the driver must keep up to
      date the last receive time, dev->last_rx, and transmit start time,
      dev->trans_start.  If these are not updated by the driver, then the
      ARP monitor will immediately fail any slaves using that driver, and
      those slaves will stay down.  If networking monitoring (tcpdump, etc)
      shows the ARP requests and replies on the network, then it may be that
      your device driver is not updating last_rx and trans_start.
      
      7.2 Configuring Multiple ARP Targets
      ------------------------------------
      
      	While ARP monitoring can be done with just one target, it can
      be useful in a High Availability setup to have several targets to
      monitor.  In the case of just one target, the target itself may go
      down or have a problem making it unresponsive to ARP requests.  Having
      an additional target (or several) increases the reliability of the ARP
      monitoring.
      
      	Multiple ARP targets must be separated by commas as follows:
      
      # example options for ARP monitoring with three targets
      alias bond0 bonding
      options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9
      
      	For just a single target the options would resemble:
      
      # example options for ARP monitoring with one target
      alias bond0 bonding
      options bond0 arp_interval=60 arp_ip_target=192.168.0.100
      
      
      7.3 MII Monitor Operation
      -------------------------
      
      	The MII monitor monitors only the carrier state of the local
      network interface.  It accomplishes this in one of three ways: by
      depending upon the device driver to maintain its carrier state, by
      querying the device's MII registers, or by making an ethtool query to
      the device.
      
      	If the use_carrier module parameter is 1 (the default value),
      then the MII monitor will rely on the driver for carrier state
      information (via the netif_carrier subsystem).  As explained in the
      use_carrier parameter information, above, if the MII monitor fails to
      detect carrier loss on the device (e.g., when the cable is physically
      disconnected), it may be that the driver does not support
      netif_carrier.
      
      	If use_carrier is 0, then the MII monitor will first query the
      device's (via ioctl) MII registers and check the link state.  If that
      request fails (not just that it returns carrier down), then the MII
      monitor will make an ethtool ETHOOL_GLINK request to attempt to obtain
      the same information.  If both methods fail (i.e., the driver either
      does not support or had some error in processing both the MII register
      and ethtool requests), then the MII monitor will assume the link is
      up.
      
      8. Potential Sources of Trouble
      ===============================
      
      8.1 Adventures in Routing
      -------------------------
      
      	When bonding is configured, it is important that the slave
      devices not have routes that supersede routes of the master (or,
      generally, not have routes at all).  For example, suppose the bonding
      device bond0 has two slaves, eth0 and eth1, and the routing table is
      as follows:
      
      Kernel IP routing table
      Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
      10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth0
      10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth1
      10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 bond0
      127.0.0.0       0.0.0.0         255.0.0.0       U        40 0          0 lo
      
      	This routing configuration will likely still update the
      receive/transmit times in the driver (needed by the ARP monitor), but
      may bypass the bonding driver (because outgoing traffic to, in this
      case, another host on network 10 would use eth0 or eth1 before bond0).
      
      	The ARP monitor (and ARP itself) may become confused by this
      configuration, because ARP requests (generated by the ARP monitor)
      will be sent on one interface (bond0), but the corresponding reply
      will arrive on a different interface (eth0).  This reply looks to ARP
      as an unsolicited ARP reply (because ARP matches replies on an
      interface basis), and is discarded.  The MII monitor is not affected
      by the state of the routing table.
      
      	The solution here is simply to insure that slaves do not have
      routes of their own, and if for some reason they must, those routes do
      not supersede routes of their master.  This should generally be the
      case, but unusual configurations or errant manual or automatic static
      route additions may cause trouble.
      
      8.2 Ethernet Device Renaming
      ----------------------------
      
      	On systems with network configuration scripts that do not
      associate physical devices directly with network interface names (so
      that the same physical device always has the same "ethX" name), it may
      be necessary to add some special logic to either /etc/modules.conf or
      /etc/modprobe.conf (depending upon which is installed on the system).
      
      	For example, given a modules.conf containing the following:
      
      alias bond0 bonding
      options bond0 mode=some-mode miimon=50
      alias eth0 tg3
      alias eth1 tg3
      alias eth2 e1000
      alias eth3 e1000
      
      	If neither eth0 and eth1 are slaves to bond0, then when the
      bond0 interface comes up, the devices may end up reordered.  This
      happens because bonding is loaded first, then its slave device's
      drivers are loaded next.  Since no other drivers have been loaded,
      when the e1000 driver loads, it will receive eth0 and eth1 for its
      devices, but the bonding configuration tries to enslave eth2 and eth3
      (which may later be assigned to the tg3 devices).
      
      	Adding the following:
      
      add above bonding e1000 tg3
      
      	causes modprobe to load e1000 then tg3, in that order, when
      bonding is loaded.  This command is fully documented in the
      modules.conf manual page.
      
      	On systems utilizing modprobe.conf (or modprobe.conf.local),
      an equivalent problem can occur.  In this case, the following can be
      added to modprobe.conf (or modprobe.conf.local, as appropriate), as
      follows (all on one line; it has been split here for clarity):
      
      install bonding /sbin/modprobe tg3; /sbin/modprobe e1000;
      	/sbin/modprobe --ignore-install bonding
      
      	This will, when loading the bonding module, rather than
      performing the normal action, instead execute the provided command.
      This command loads the device drivers in the order needed, then calls
      modprobe with --ignore-install to cause the normal action to then take
      place.  Full documentation on this can be found in the modprobe.conf
      and modprobe manual pages.
      
      8.3. Painfully Slow Or No Failed Link Detection By Miimon
      ---------------------------------------------------------
      
      	By default, bonding enables the use_carrier option, which
      instructs bonding to trust the driver to maintain carrier state.
      
      	As discussed in the options section, above, some drivers do
      not support the netif_carrier_on/_off link state tracking system.
      With use_carrier enabled, bonding will always see these links as up,
      regardless of their actual state.
      
      	Additionally, other drivers do support netif_carrier, but do
      not maintain it in real time, e.g., only polling the link state at
      some fixed interval.  In this case, miimon will detect failures, but
      only after some long period of time has expired.  If it appears that
      miimon is very slow in detecting link failures, try specifying
      use_carrier=0 to see if that improves the failure detection time.  If
      it does, then it may be that the driver checks the carrier state at a
      fixed interval, but does not cache the MII register values (so the
      use_carrier=0 method of querying the registers directly works).  If
      use_carrier=0 does not improve the failover, then the driver may cache
      the registers, or the problem may be elsewhere.
      
      	Also, remember that miimon only checks for the device's
      carrier state.  It has no way to determine the state of devices on or
      beyond other ports of a switch, or if a switch is refusing to pass
      traffic while still maintaining carrier on.
      
      9. SNMP agents
      ===============
      
      	If running SNMP agents, the bonding driver should be loaded
      before any network drivers participating in a bond.  This requirement
      is due to the interface index (ipAdEntIfIndex) being associated to
      the first interface found with a given IP address.  That is, there is
      only one ipAdEntIfIndex for each IP address.  For example, if eth0 and
      eth1 are slaves of bond0 and the driver for eth0 is loaded before the
      bonding driver, the interface for the IP address will be associated
      with the eth0 interface.  This configuration is shown below, the IP
      address 192.168.1.1 has an interface index of 2 which indexes to eth0
      in the ifDescr table (ifDescr.2).
      
           interfaces.ifTable.ifEntry.ifDescr.1 = lo
           interfaces.ifTable.ifEntry.ifDescr.2 = eth0
           interfaces.ifTable.ifEntry.ifDescr.3 = eth1
           interfaces.ifTable.ifEntry.ifDescr.4 = eth2
           interfaces.ifTable.ifEntry.ifDescr.5 = eth3
           interfaces.ifTable.ifEntry.ifDescr.6 = bond0
           ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5
           ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
           ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4
           ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
      
      	This problem is avoided by loading the bonding driver before
      any network drivers participating in a bond.  Below is an example of
      loading the bonding driver first, the IP address 192.168.1.1 is
      correctly associated with ifDescr.2.
      
           interfaces.ifTable.ifEntry.ifDescr.1 = lo
           interfaces.ifTable.ifEntry.ifDescr.2 = bond0
           interfaces.ifTable.ifEntry.ifDescr.3 = eth0
           interfaces.ifTable.ifEntry.ifDescr.4 = eth1
           interfaces.ifTable.ifEntry.ifDescr.5 = eth2
           interfaces.ifTable.ifEntry.ifDescr.6 = eth3
           ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6
           ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
           ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5
           ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1
      
      	While some distributions may not report the interface name in
      ifDescr, the association between the IP address and IfIndex remains
      and SNMP functions such as Interface_Scan_Next will report that
      association.
      
      10. Promiscuous mode
      ====================
      
      	When running network monitoring tools, e.g., tcpdump, it is
      common to enable promiscuous mode on the device, so that all traffic
      is seen (instead of seeing only traffic destined for the local host).
      The bonding driver handles promiscuous mode changes to the bonding
      master device (e.g., bond0), and propagates the setting to the slave
      devices.
      
      	For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
      the promiscuous mode setting is propagated to all slaves.
      
      	For the active-backup, balance-tlb and balance-alb modes, the
      promiscuous mode setting is propagated only to the active slave.
      
      	For balance-tlb mode, the active slave is the slave currently
      receiving inbound traffic.
      
      	For balance-alb mode, the active slave is the slave used as a
      "primary."  This slave is used for mode-specific control traffic, for
      sending to peers that are unassigned or if the load is unbalanced.
      
      	For the active-backup, balance-tlb and balance-alb modes, when
      the active slave changes (e.g., due to a link failure), the
      promiscuous setting will be propagated to the new active slave.
      
      11. Configuring Bonding for High Availability
      =============================================
      
      	High Availability refers to configurations that provide
      maximum network availability by having redundant or backup devices,
      links or switches between the host and the rest of the world.  The
      goal is to provide the maximum availability of network connectivity
      (i.e., the network always works), even though other configurations
      could provide higher throughput.
      
      11.1 High Availability in a Single Switch Topology
      --------------------------------------------------
      
      	If two hosts (or a host and a single switch) are directly
      connected via multiple physical links, then there is no availability
      penalty to optimizing for maximum bandwidth.  In this case, there is
      only one switch (or peer), so if it fails, there is no alternative
      access to fail over to.  Additionally, the bonding load balance modes
      support link monitoring of their members, so if individual links fail,
      the load will be rebalanced across the remaining devices.
      
      	See Section 13, "Configuring Bonding for Maximum Throughput"
      for information on configuring bonding with one peer device.
      
      11.2 High Availability in a Multiple Switch Topology
      ----------------------------------------------------
      
      	With multiple switches, the configuration of bonding and the
      network changes dramatically.  In multiple switch topologies, there is
      a trade off between network availability and usable bandwidth.
      
      	Below is a sample network, configured to maximize the
      availability of the network:
      
                      |                                     |
                      |port3                           port3|
                +-----+----+                          +-----+----+
                |          |port2       ISL      port2|          |
                | switch A +--------------------------+ switch B |
                |          |                          |          |
                +-----+----+                          +-----++---+
                      |port1                           port1|
                      |             +-------+               |
                      +-------------+ host1 +---------------+
                               eth0 +-------+ eth1
      
      	In this configuration, there is a link between the two
      switches (ISL, or inter switch link), and multiple ports connecting to
      the outside world ("port3" on each switch).  There is no technical
      reason that this could not be extended to a third switch.
      
      11.2.1 HA Bonding Mode Selection for Multiple Switch Topology
      -------------------------------------------------------------
      
      	In a topology such as the example above, the active-backup and
      broadcast modes are the only useful bonding modes when optimizing for
      availability; the other modes require all links to terminate on the
      same peer for them to behave rationally.
      
      active-backup: This is generally the preferred mode, particularly if
      	the switches have an ISL and play together well.  If the
      	network configuration is such that one switch is specifically
      	a backup switch (e.g., has lower capacity, higher cost, etc),
      	then the primary option can be used to insure that the
      	preferred link is always used when it is available.
      
      broadcast: This mode is really a special purpose mode, and is suitable
      	only for very specific needs.  For example, if the two
      	switches are not connected (no ISL), and the networks beyond
      	them are totally independent.  In this case, if it is
      	necessary for some specific one-way traffic to reach both
      	independent networks, then the broadcast mode may be suitable.
      
      11.2.2 HA Link Monitoring Selection for Multiple Switch Topology
      ----------------------------------------------------------------
      
      	The choice of link monitoring ultimately depends upon your
      switch.  If the switch can reliably fail ports in response to other
      failures, then either the MII or ARP monitors should work.  For
      example, in the above example, if the "port3" link fails at the remote
      end, the MII monitor has no direct means to detect this.  The ARP
      monitor could be configured with a target at the remote end of port3,
      thus detecting that failure without switch support.
      
      	In general, however, in a multiple switch topology, the ARP
      monitor can provide a higher level of reliability in detecting end to
      end connectivity failures (which may be caused by the failure of any
      individual component to pass traffic for any reason).  Additionally,
      the ARP monitor should be configured with multiple targets (at least
      one for each switch in the network).  This will insure that,
      regardless of which switch is active, the ARP monitor has a suitable
      target to query.
      
      	Note, also, that of late many switches now support a functionality
      generally referred to as "trunk failover."  This is a feature of the
      switch that causes the link state of a particular switch port to be set
      down (or up) when the state of another switch port goes down (or up).
      Its purpose is to propagate link failures from logically "exterior" ports
      to the logically "interior" ports that bonding is able to monitor via
      miimon.  Availability and configuration for trunk failover varies by
      switch, but this can be a viable alternative to the ARP monitor when using
      suitable switches.
      
      12. Configuring Bonding for Maximum Throughput
      ==============================================
      
      12.1 Maximizing Throughput in a Single Switch Topology
      ------------------------------------------------------
      
      	In a single switch configuration, the best method to maximize
      throughput depends upon the application and network environment.  The
      various load balancing modes each have strengths and weaknesses in
      different environments, as detailed below.
      
      	For this discussion, we will break down the topologies into
      two categories.  Depending upon the destination of most traffic, we
      categorize them into either "gatewayed" or "local" configurations.
      
      	In a gatewayed configuration, the "switch" is acting primarily
      as a router, and the majority of traffic passes through this router to
      other networks.  An example would be the following:
      
      
           +----------+                     +----------+
           |          |eth0            port1|          | to other networks
           | Host A   +---------------------+ router   +------------------->
           |          +---------------------+          | Hosts B and C are out
           |          |eth1            port2|          | here somewhere
           +----------+                     +----------+
      
      	The router may be a dedicated router device, or another host
      acting as a gateway.  For our discussion, the important point is that
      the majority of traffic from Host A will pass through the router to
      some other network before reaching its final destination.
      
      	In a gatewayed network configuration, although Host A may
      communicate with many other systems, all of its traffic will be sent
      and received via one other peer on the local network, the router.
      
      	Note that the case of two systems connected directly via
      multiple physical links is, for purposes of configuring bonding, the
      same as a gatewayed configuration.  In that case, it happens that all
      traffic is destined for the "gateway" itself, not some other network
      beyond the gateway.
      
      	In a local configuration, the "switch" is acting primarily as
      a switch, and the majority of traffic passes through this switch to
      reach other stations on the same network.  An example would be the
      following:
      
          +----------+            +----------+       +--------+
          |          |eth0   port1|          +-------+ Host B |
          |  Host A  +------------+  switch  |port3  +--------+
          |          +------------+          |                  +--------+
          |          |eth1   port2|          +------------------+ Host C |
          +----------+            +----------+port4             +--------+
      
      
      	Again, the switch may be a dedicated switch device, or another
      host acting as a gateway.  For our discussion, the important point is
      that the majority of traffic from Host A is destined for other hosts
      on the same local network (Hosts B and C in the above example).
      
      	In summary, in a gatewayed configuration, traffic to and from
      the bonded device will be to the same MAC level peer on the network
      (the gateway itself, i.e., the router), regardless of its final
      destination.  In a local configuration, traffic flows directly to and
      from the final destinations, thus, each destination (Host B, Host C)
      will be addressed directly by their individual MAC addresses.
      
      	This distinction between a gatewayed and a local network
      configuration is important because many of the load balancing modes
      available use the MAC addresses of the local network source and
      destination to make load balancing decisions.  The behavior of each
      mode is described below.
      
      
      12.1.1 MT Bonding Mode Selection for Single Switch Topology
      -----------------------------------------------------------
      
      	This configuration is the easiest to set up and to understand,
      although you will have to decide which bonding mode best suits your
      needs.  The trade offs for each mode are detailed below:
      
      balance-rr: This mode is the only mode that will permit a single
      	TCP/IP connection to stripe traffic across multiple
      	interfaces. It is therefore the only mode that will allow a
      	single TCP/IP stream to utilize more than one interface's
      	worth of throughput.  This comes at a cost, however: the
      	striping generally results in peer systems receiving packets out
      	of order, causing TCP/IP's congestion control system to kick
      	in, often by retransmitting segments.
      
      	It is possible to adjust TCP/IP's congestion limits by
      	altering the net.ipv4.tcp_reordering sysctl parameter.  The
      	usual default value is 3, and the maximum useful value is 127.
      	For a four interface balance-rr bond, expect that a single
      	TCP/IP stream will utilize no more than approximately 2.3
      	interface's worth of throughput, even after adjusting
      	tcp_reordering.
      
      	Note that the fraction of packets that will be delivered out of
      	order is highly variable, and is unlikely to be zero.  The level
      	of reordering depends upon a variety of factors, including the
      	networking interfaces, the switch, and the topology of the
      	configuration.  Speaking in general terms, higher speed network
      	cards produce more reordering (due to factors such as packet
      	coalescing), and a "many to many" topology will reorder at a
      	higher rate than a "many slow to one fast" configuration.
      
      	Many switches do not support any modes that stripe traffic
      	(instead choosing a port based upon IP or MAC level addresses);
      	for those devices, traffic for a particular connection flowing
      	through the switch to a balance-rr bond will not utilize greater
      	than one interface's worth of bandwidth.
      
      	If you are utilizing protocols other than TCP/IP, UDP for
      	example, and your application can tolerate out of order
      	delivery, then this mode can allow for single stream datagram
      	performance that scales near linearly as interfaces are added
      	to the bond.
      
      	This mode requires the switch to have the appropriate ports
      	configured for "etherchannel" or "trunking."
      
      active-backup: There is not much advantage in this network topology to
      	the active-backup mode, as the inactive backup devices are all
      	connected to the same peer as the primary.  In this case, a
      	load balancing mode (with link monitoring) will provide the
      	same level of network availability, but with increased
      	available bandwidth.  On the plus side, active-backup mode
      	does not require any configuration of the switch, so it may
      	have value if the hardware available does not support any of
      	the load balance modes.
      
      balance-xor: This mode will limit traffic such that packets destined
      	for specific peers will always be sent over the same
      	interface.  Since the destination is determined by the MAC
      	addresses involved, this mode works best in a "local" network
      	configuration (as described above), with destinations all on
      	the same local network.  This mode is likely to be suboptimal
      	if all your traffic is passed through a single router (i.e., a
      	"gatewayed" network configuration, as described above).
      
      	As with balance-rr, the switch ports need to be configured for
      	"etherchannel" or "trunking."
      
      broadcast: Like active-backup, there is not much advantage to this
      	mode in this type of network topology.
      
      802.3ad: This mode can be a good choice for this type of network
      	topology.  The 802.3ad mode is an IEEE standard, so all peers
      	that implement 802.3ad should interoperate well.  The 802.3ad
      	protocol includes automatic configuration of the aggregates,
      	so minimal manual configuration of the switch is needed
      	(typically only to designate that some set of devices is
      	available for 802.3ad).  The 802.3ad standard also mandates
      	that frames be delivered in order (within certain limits), so
      	in general single connections will not see misordering of
      	packets.  The 802.3ad mode does have some drawbacks: the
      	standard mandates that all devices in the aggregate operate at
      	the same speed and duplex.  Also, as with all bonding load
      	balance modes other than balance-rr, no single connection will
      	be able to utilize more than a single interface's worth of
      	bandwidth.  
      
      	Additionally, the linux bonding 802.3ad implementation
      	distributes traffic by peer (using an XOR of MAC addresses),
      	so in a "gatewayed" configuration, all outgoing traffic will
      	generally use the same device.  Incoming traffic may also end
      	up on a single device, but that is dependent upon the
      	balancing policy of the peer's 8023.ad implementation.  In a
      	"local" configuration, traffic will be distributed across the
      	devices in the bond.
      
      	Finally, the 802.3ad mode mandates the use of the MII monitor,
      	therefore, the ARP monitor is not available in this mode.
      
      balance-tlb: The balance-tlb mode balances outgoing traffic by peer.
      	Since the balancing is done according to MAC address, in a
      	"gatewayed" configuration (as described above), this mode will
      	send all traffic across a single device.  However, in a
      	"local" network configuration, this mode balances multiple
      	local network peers across devices in a vaguely intelligent
      	manner (not a simple XOR as in balance-xor or 802.3ad mode),
      	so that mathematically unlucky MAC addresses (i.e., ones that
      	XOR to the same value) will not all "bunch up" on a single
      	interface.
      
      	Unlike 802.3ad, interfaces may be of differing speeds, and no
      	special switch configuration is required.  On the down side,
      	in this mode all incoming traffic arrives over a single
      	interface, this mode requires certain ethtool support in the
      	network device driver of the slave interfaces, and the ARP
      	monitor is not available.
      
      balance-alb: This mode is everything that balance-tlb is, and more.
      	It has all of the features (and restrictions) of balance-tlb,
      	and will also balance incoming traffic from local network
      	peers (as described in the Bonding Module Options section,
      	above).
      
      	The only additional down side to this mode is that the network
      	device driver must support changing the hardware address while
      	the device is open.
      
      12.1.2 MT Link Monitoring for Single Switch Topology
      ----------------------------------------------------
      
      	The choice of link monitoring may largely depend upon which
      mode you choose to use.  The more advanced load balancing modes do not
      support the use of the ARP monitor, and are thus restricted to using
      the MII monitor (which does not provide as high a level of end to end
      assurance as the ARP monitor).
      
      12.2 Maximum Throughput in a Multiple Switch Topology
      -----------------------------------------------------
      
      	Multiple switches may be utilized to optimize for throughput
      when they are configured in parallel as part of an isolated network
      between two or more systems, for example:
      
                             +-----------+
                             |  Host A   | 
                             +-+---+---+-+
                               |   |   |
                      +--------+   |   +---------+
                      |            |             |
               +------+---+  +-----+----+  +-----+----+
               | Switch A |  | Switch B |  | Switch C |
               +------+---+  +-----+----+  +-----+----+
                      |            |             |
                      +--------+   |   +---------+
                               |   |   |
                             +-+---+---+-+
                             |  Host B   | 
                             +-----------+
      
      	In this configuration, the switches are isolated from one
      another.  One reason to employ a topology such as this is for an
      isolated network with many hosts (a cluster configured for high
      performance, for example), using multiple smaller switches can be more
      cost effective than a single larger switch, e.g., on a network with 24
      hosts, three 24 port switches can be significantly less expensive than
      a single 72 port switch.
      
      	If access beyond the network is required, an individual host
      can be equipped with an additional network device connected to an
      external network; this host then additionally acts as a gateway.
      
      12.2.1 MT Bonding Mode Selection for Multiple Switch Topology
      -------------------------------------------------------------
      
      	In actual practice, the bonding mode typically employed in
      configurations of this type is balance-rr.  Historically, in this
      network configuration, the usual caveats about out of order packet
      delivery are mitigated by the use of network adapters that do not do
      any kind of packet coalescing (via the use of NAPI, or because the
      device itself does not generate interrupts until some number of
      packets has arrived).  When employed in this fashion, the balance-rr
      mode allows individual connections between two hosts to effectively
      utilize greater than one interface's bandwidth.
      
      12.2.2 MT Link Monitoring for Multiple Switch Topology
      ------------------------------------------------------
      
      	Again, in actual practice, the MII monitor is most often used
      in this configuration, as performance is given preference over
      availability.  The ARP monitor will function in this topology, but its
      advantages over the MII monitor are mitigated by the volume of probes
      needed as the number of systems involved grows (remember that each
      host in the network is configured with bonding).
      
      13. Switch Behavior Issues
      ==========================
      
      13.1 Link Establishment and Failover Delays
      -------------------------------------------
      
      	Some switches exhibit undesirable behavior with regard to the
      timing of link up and down reporting by the switch.
      
      	First, when a link comes up, some switches may indicate that
      the link is up (carrier available), but not pass traffic over the
      interface for some period of time.  This delay is typically due to
      some type of autonegotiation or routing protocol, but may also occur
      during switch initialization (e.g., during recovery after a switch
      failure).  If you find this to be a problem, specify an appropriate
      value to the updelay bonding module option to delay the use of the
      relevant interface(s).
      
      	Second, some switches may "bounce" the link state one or more
      times while a link is changing state.  This occurs most commonly while
      the switch is initializing.  Again, an appropriate updelay value may
      help.
      
      	Note that when a bonding interface has no active links, the
      driver will immediately reuse the first link that goes up, even if the
      updelay parameter has been specified (the updelay is ignored in this
      case).  If there are slave interfaces waiting for the updelay timeout
      to expire, the interface that first went into that state will be
      immediately reused.  This reduces down time of the network if the
      value of updelay has been overestimated, and since this occurs only in
      cases with no connectivity, there is no additional penalty for
      ignoring the updelay.
      
      	In addition to the concerns about switch timings, if your
      switches take a long time to go into backup mode, it may be desirable
      to not activate a backup interface immediately after a link goes down.
      Failover may be delayed via the downdelay bonding module option.
      
      13.2 Duplicated Incoming Packets
      --------------------------------
      
      	NOTE: Starting with version 3.0.2, the bonding driver has logic to
      suppress duplicate packets, which should largely eliminate this problem.
      The following description is kept for reference.
      
      	It is not uncommon to observe a short burst of duplicated
      traffic when the bonding device is first used, or after it has been
      idle for some period of time.  This is most easily observed by issuing
      a "ping" to some other host on the network, and noticing that the
      output from ping flags duplicates (typically one per slave).
      
      	For example, on a bond in active-backup mode with five slaves
      all connected to one switch, the output may appear as follows:
      
      # ping -n 10.0.4.2
      PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data.
      64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms
      64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
      64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
      64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
      64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
      64 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms
      64 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms
      64 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms
      
      	This is not due to an error in the bonding driver, rather, it
      is a side effect of how many switches update their MAC forwarding
      tables.  Initially, the switch does not associate the MAC address in
      the packet with a particular switch port, and so it may send the
      traffic to all ports until its MAC forwarding table is updated.  Since
      the interfaces attached to the bond may occupy multiple ports on a
      single switch, when the switch (temporarily) floods the traffic to all
      ports, the bond device receives multiple copies of the same packet
      (one per slave device).
      
      	The duplicated packet behavior is switch dependent, some
      switches exhibit this, and some do not.  On switches that display this
      behavior, it can be induced by clearing the MAC forwarding table (on
      most Cisco switches, the privileged command "clear mac address-table
      dynamic" will accomplish this).
      
      14. Hardware Specific Considerations
      ====================================
      
      	This section contains additional information for configuring
      bonding on specific hardware platforms, or for interfacing bonding
      with particular switches or other devices.
      
      14.1 IBM BladeCenter
      --------------------
      
      	This applies to the JS20 and similar systems.
      
      	On the JS20 blades, the bonding driver supports only
      balance-rr, active-backup, balance-tlb and balance-alb modes.  This is
      largely due to the network topology inside the BladeCenter, detailed
      below.
      
      JS20 network adapter information
      --------------------------------
      
      	All JS20s come with two Broadcom Gigabit Ethernet ports
      integrated on the planar (that's "motherboard" in IBM-speak).  In the
      BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to
      I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2.
      An add-on Broadcom daughter card can be installed on a JS20 to provide
      two more Gigabit Ethernet ports.  These ports, eth2 and eth3, are
      wired to I/O Modules 3 and 4, respectively.
      
      	Each I/O Module may contain either a switch or a passthrough
      module (which allows ports to be directly connected to an external
      switch).  Some bonding modes require a specific BladeCenter internal
      network topology in order to function; these are detailed below.
      
      	Additional BladeCenter-specific networking information can be
      found in two IBM Redbooks (www.ibm.com/redbooks):
      
      "IBM eServer BladeCenter Networking Options"
      "IBM eServer BladeCenter Layer 2-7 Network Switching"
      
      BladeCenter networking configuration
      ------------------------------------
      
      	Because a BladeCenter can be configured in a very large number
      of ways, this discussion will be confined to describing basic
      configurations.
      
      	Normally, Ethernet Switch Modules (ESMs) are used in I/O
      modules 1 and 2.  In this configuration, the eth0 and eth1 ports of a
      JS20 will be connected to different internal switches (in the
      respective I/O modules).
      
      	A passthrough module (OPM or CPM, optical or copper,
      passthrough module) connects the I/O module directly to an external
      switch.  By using PMs in I/O module #1 and #2, the eth0 and eth1
      interfaces of a JS20 can be redirected to the outside world and
      connected to a common external switch.
      
      	Depending upon the mix of ESMs and PMs, the network will
      appear to bonding as either a single switch topology (all PMs) or as a
      multiple switch topology (one or more ESMs, zero or more PMs).  It is
      also possible to connect ESMs together, resulting in a configuration
      much like the example in "High Availability in a Multiple Switch
      Topology," above.
      
      Requirements for specific modes
      -------------------------------
      
      	The balance-rr mode requires the use of passthrough modules
      for devices in the bond, all connected to an common external switch.
      That switch must be configured for "etherchannel" or "trunking" on the
      appropriate ports, as is usual for balance-rr.
      
      	The balance-alb and balance-tlb modes will function with
      either switch modules or passthrough modules (or a mix).  The only
      specific requirement for these modes is that all network interfaces
      must be able to reach all destinations for traffic sent over the
      bonding device (i.e., the network must converge at some point outside
      the BladeCenter).
      
      	The active-backup mode has no additional requirements.
      
      Link monitoring issues
      ----------------------
      
      	When an Ethernet Switch Module is in place, only the ARP
      monitor will reliably detect link loss to an external switch.  This is
      nothing unusual, but examination of the BladeCenter cabinet would
      suggest that the "external" network ports are the ethernet ports for
      the system, when it fact there is a switch between these "external"
      ports and the devices on the JS20 system itself.  The MII monitor is
      only able to detect link failures between the ESM and the JS20 system.
      
      	When a passthrough module is in place, the MII monitor does
      detect failures to the "external" port, which is then directly
      connected to the JS20 system.
      
      Other concerns
      --------------
      
      	The Serial Over LAN (SoL) link is established over the primary
      ethernet (eth0) only, therefore, any loss of link to eth0 will result
      in losing your SoL connection.  It will not fail over with other
      network traffic, as the SoL system is beyond the control of the
      bonding driver.
      
      	It may be desirable to disable spanning tree on the switch
      (either the internal Ethernet Switch Module, or an external switch) to
      avoid fail-over delay issues when using bonding.
      
      	
      15. Frequently Asked Questions
      ==============================
      
      1.  Is it SMP safe?
      
      	Yes. The old 2.0.xx channel bonding patch was not SMP safe.
      The new driver was designed to be SMP safe from the start.
      
      2.  What type of cards will work with it?
      
      	Any Ethernet type cards (you can even mix cards - a Intel
      EtherExpress PRO/100 and a 3com 3c905b, for example).  For most modes,
      devices need not be of the same speed.
      
      	Starting with version 3.2.1, bonding also supports Infiniband
      slaves in active-backup mode.
      
      3.  How many bonding devices can I have?
      
      	There is no limit.
      
      4.  How many slaves can a bonding device have?
      
      	This is limited only by the number of network interfaces Linux
      supports and/or the number of network cards you can place in your
      system.
      
      5.  What happens when a slave link dies?
      
      	If link monitoring is enabled, then the failing device will be
      disabled.  The active-backup mode will fail over to a backup link, and
      other modes will ignore the failed link.  The link will continue to be
      monitored, and should it recover, it will rejoin the bond (in whatever
      manner is appropriate for the mode). See the sections on High
      Availability and the documentation for each mode for additional
      information.
      	
      	Link monitoring can be enabled via either the miimon or
      arp_interval parameters (described in the module parameters section,
      above).  In general, miimon monitors the carrier state as sensed by
      the underlying network device, and the arp monitor (arp_interval)
      monitors connectivity to another host on the local network.
      
      	If no link monitoring is configured, the bonding driver will
      be unable to detect link failures, and will assume that all links are
      always available.  This will likely result in lost packets, and a
      resulting degradation of performance.  The precise performance loss
      depends upon the bonding mode and network configuration.
      
      6.  Can bonding be used for High Availability?
      
      	Yes.  See the section on High Availability for details.
      
      7.  Which switches/systems does it work with?
      
      	The full answer to this depends upon the desired mode.
      
      	In the basic balance modes (balance-rr and balance-xor), it
      works with any system that supports etherchannel (also called
      trunking).  Most managed switches currently available have such
      support, and many unmanaged switches as well.
      
      	The advanced balance modes (balance-tlb and balance-alb) do
      not have special switch requirements, but do need device drivers that
      support specific features (described in the appropriate section under
      module parameters, above).
      
      	In 802.3ad mode, it works with systems that support IEEE
      802.3ad Dynamic Link Aggregation.  Most managed and many unmanaged
      switches currently available support 802.3ad.
      
              The active-backup mode should work with any Layer-II switch.
      
      8.  Where does a bonding device get its MAC address from?
      
      	When using slave devices that have fixed MAC addresses, or when
      the fail_over_mac option is enabled, the bonding device's MAC address is
      the MAC address of the active slave.
      
      	For other configurations, if not explicitly configured (with
      ifconfig or ip link), the MAC address of the bonding device is taken from
      its first slave device.  This MAC address is then passed to all following
      slaves and remains persistent (even if the first slave is removed) until
      the bonding device is brought down or reconfigured.
      
      	If you wish to change the MAC address, you can set it with
      ifconfig or ip link:
      
      # ifconfig bond0 hw ether 00:11:22:33:44:55
      
      # ip link set bond0 address 66:77:88:99:aa:bb
      
      	The MAC address can be also changed by bringing down/up the
      device and then changing its slaves (or their order):
      
      # ifconfig bond0 down ; modprobe -r bonding
      # ifconfig bond0 .... up
      # ifenslave bond0 eth...
      
      	This method will automatically take the address from the next
      slave that is added.
      
      	To restore your slaves' MAC addresses, you need to detach them
      from the bond (`ifenslave -d bond0 eth0'). The bonding driver will
      then restore the MAC addresses that the slaves had before they were
      enslaved.
      
      16. Resources and Links
      =======================
      
      	The latest version of the bonding driver can be found in the latest
      version of the linux kernel, found on http://kernel.org
      
      	The latest version of this document can be found in the latest kernel
      source (named Documentation/networking/bonding.txt).
      
      	Discussions regarding the usage of the bonding driver take place on the
      bonding-devel mailing list, hosted at sourceforge.net. If you have questions or
      problems, post them to the list.  The list address is:
      
      [email protected]
      
      	The administrative interface (to subscribe or unsubscribe) can
      be found at:
      
      https://lists.sourceforge.net/lists/listinfo/bonding-devel
      
      	Discussions regarding the developpement of the bonding driver take place
      on the main Linux network mailing list, hosted at vger.kernel.org. The list
      address is:
      
      [email protected]
      
      	The administrative interface (to subscribe or unsubscribe) can
      be found at:
      
      http://vger.kernel.org/vger-lists.html#netdev
      
      Donald Becker's Ethernet Drivers and diag programs may be found at :
       - http://web.archive.org/web/*/http://www.scyld.com/network/ 
      
      You will also find a lot of information regarding Ethernet, NWay, MII,
      etc. at www.scyld.com.
      
      -- END -- 
		Linux Ethernet Bonding Driver HOWTO

		Latest update: 27 April 2011

Initial release : Thomas Davis 
Corrections, HA extensions : 2000/10/03-15 :
  - Willy Tarreau 
  - Constantine Gavrilov 
  - Chad N. Tindel 
  - Janice Girouard 
  - Jay Vosburgh 

Reorganized and updated Feb 2005 by Jay Vosburgh
Added Sysfs information: 2006/04/24
  - Mitch Williams 

Introduction
============

	The Linux bonding driver provides a method for aggregating
multiple network interfaces into a single logical "bonded" interface.
The behavior of the bonded interfaces depends upon the mode; generally
speaking, modes provide either hot standby or load balancing services.
Additionally, link integrity monitoring may be performed.
	
	The bonding driver originally came from Donald Becker's
beowulf patches for kernel 2.0. It has changed quite a bit since, and
the original tools from extreme-linux and beowulf sites will not work
with this version of the driver.

	For new versions of the driver, updated userspace tools, and
who to ask for help, please follow the links at the end of this file.

Table of Contents
=================

1. Bonding Driver Installation

2. Bonding Driver Options

3. Configuring Bonding Devices
3.1	Configuration with Sysconfig Support
3.1.1		Using DHCP with Sysconfig
3.1.2		Configuring Multiple Bonds with Sysconfig
3.2	Configuration with Initscripts Support
3.2.1		Using DHCP with Initscripts
3.2.2		Configuring Multiple Bonds with Initscripts
3.3	Configuring Bonding Manually with Ifenslave
3.3.1		Configuring Multiple Bonds Manually
3.4	Configuring Bonding Manually via Sysfs
3.5	Configuration with Interfaces Support
3.6	Overriding Configuration for Special Cases

4. Querying Bonding Configuration
4.1	Bonding Configuration
4.2	Network Configuration

5. Switch Configuration

6. 802.1q VLAN Support

7. Link Monitoring
7.1	ARP Monitor Operation
7.2	Configuring Multiple ARP Targets
7.3	MII Monitor Operation

8. Potential Trouble Sources
8.1	Adventures in Routing
8.2	Ethernet Device Renaming
8.3	Painfully Slow Or No Failed Link Detection By Miimon

9. SNMP agents

10. Promiscuous mode

11. Configuring Bonding for High Availability
11.1	High Availability in a Single Switch Topology
11.2	High Availability in a Multiple Switch Topology
11.2.1		HA Bonding Mode Selection for Multiple Switch Topology
11.2.2		HA Link Monitoring for Multiple Switch Topology

12. Configuring Bonding for Maximum Throughput
12.1	Maximum Throughput in a Single Switch Topology
12.1.1		MT Bonding Mode Selection for Single Switch Topology
12.1.2		MT Link Monitoring for Single Switch Topology
12.2	Maximum Throughput in a Multiple Switch Topology
12.2.1		MT Bonding Mode Selection for Multiple Switch Topology
12.2.2		MT Link Monitoring for Multiple Switch Topology

13. Switch Behavior Issues
13.1	Link Establishment and Failover Delays
13.2	Duplicated Incoming Packets

14. Hardware Specific Considerations
14.1	IBM BladeCenter

15. Frequently Asked Questions

16. Resources and Links


1. Bonding Driver Installation
==============================

	Most popular distro kernels ship with the bonding driver
already available as a module and the ifenslave user level control
program installed and ready for use. If your distro does not, or you
have need to compile bonding from source (e.g., configuring and
installing a mainline kernel from kernel.org), you'll need to perform
the following steps:

1.1 Configure and build the kernel with bonding
-----------------------------------------------

	The current version of the bonding driver is available in the
drivers/net/bonding subdirectory of the most recent kernel source
(which is available on http://kernel.org).  Most users "rolling their
own" will want to use the most recent kernel from kernel.org.

	Configure kernel with "make menuconfig" (or "make xconfig" or
"make config"), then select "Bonding driver support" in the "Network
device support" section.  It is recommended that you configure the
driver as module since it is currently the only way to pass parameters
to the driver or configure more than one bonding device.

	Build and install the new kernel and modules, then continue
below to install ifenslave.

1.2 Install ifenslave Control Utility
-------------------------------------

	The ifenslave user level control program is included in the
kernel source tree, in the file Documentation/networking/ifenslave.c.
It is generally recommended that you use the ifenslave that
corresponds to the kernel that you are using (either from the same
source tree or supplied with the distro), however, ifenslave
executables from older kernels should function (but features newer
than the ifenslave release are not supported).  Running an ifenslave
that is newer than the kernel is not supported, and may or may not
work.

	To install ifenslave, do the following:

# gcc -Wall -O -I/usr/src/linux/include ifenslave.c -o ifenslave
# cp ifenslave /sbin/ifenslave

	If your kernel source is not in "/usr/src/linux," then replace
"/usr/src/linux/include" in the above with the location of your kernel
source include directory.

	You may wish to back up any existing /sbin/ifenslave, or, for
testing or informal use, tag the ifenslave to the kernel version
(e.g., name the ifenslave executable /sbin/ifenslave-2.6.10).

IMPORTANT NOTE:

	If you omit the "-I" or specify an incorrect directory, you
may end up with an ifenslave that is incompatible with the kernel
you're trying to build it for.  Some distros (e.g., Red Hat from 7.1
onwards) do not have /usr/include/linux symbolically linked to the
default kernel source include directory.

SECOND IMPORTANT NOTE:
	If you plan to configure bonding using sysfs or using the
/etc/network/interfaces file, you do not need to use ifenslave.

2. Bonding Driver Options
=========================

	Options for the bonding driver are supplied as parameters to the
bonding module at load time, or are specified via sysfs.

	Module options may be given as command line arguments to the
insmod or modprobe command, but are usually specified in either the
/etc/modules.conf or /etc/modprobe.conf configuration file, or in a
distro-specific configuration file (some of which are detailed in the next
section).

	Details on bonding support for sysfs is provided in the
"Configuring Bonding Manually via Sysfs" section, below.

	The available bonding driver parameters are listed below. If a
parameter is not specified the default value is used.  When initially
configuring a bond, it is recommended "tail -f /var/log/messages" be
run in a separate window to watch for bonding driver error messages.

	It is critical that either the miimon or arp_interval and
arp_ip_target parameters be specified, otherwise serious network
degradation will occur during link failures.  Very few devices do not
support at least miimon, so there is really no reason not to use it.

	Options with textual values will accept either the text name
or, for backwards compatibility, the option value.  E.g.,
"mode=802.3ad" and "mode=4" set the same mode.

	The parameters are as follows:

ad_select

	Specifies the 802.3ad aggregation selection logic to use.  The
	possible values and their effects are:

	stable or 0

		The active aggregator is chosen by largest aggregate
		bandwidth.

		Reselection of the active aggregator occurs only when all
		slaves of the active aggregator are down or the active
		aggregator has no slaves.

		This is the default value.

	bandwidth or 1

		The active aggregator is chosen by largest aggregate
		bandwidth.  Reselection occurs if:

		- A slave is added to or removed from the bond

		- Any slave's link state changes

		- Any slave's 802.3ad association state changes

		- The bond's administrative state changes to up

	count or 2

		The active aggregator is chosen by the largest number of
		ports (slaves).  Reselection occurs as described under the
		"bandwidth" setting, above.

	The bandwidth and count selection policies permit failover of
	802.3ad aggregations when partial failure of the active aggregator
	occurs.  This keeps the aggregator with the highest availability
	(either in bandwidth or in number of ports) active at all times.

	This option was added in bonding version 3.4.0.

arp_interval

	Specifies the ARP link monitoring frequency in milliseconds.

	The ARP monitor works by periodically checking the slave
	devices to determine whether they have sent or received
	traffic recently (the precise criteria depends upon the
	bonding mode, and the state of the slave).  Regular traffic is
	generated via ARP probes issued for the addresses specified by
	the arp_ip_target option.

	This behavior can be modified by the arp_validate option,
	below.

	If ARP monitoring is used in an etherchannel compatible mode
	(modes 0 and 2), the switch should be configured in a mode
	that evenly distributes packets across all links. If the
	switch is configured to distribute the packets in an XOR
	fashion, all replies from the ARP targets will be received on
	the same link which could cause the other team members to
	fail.  ARP monitoring should not be used in conjunction with
	miimon.  A value of 0 disables ARP monitoring.  The default
	value is 0.

arp_ip_target

	Specifies the IP addresses to use as ARP monitoring peers when
	arp_interval is > 0.  These are the targets of the ARP request
	sent to determine the health of the link to the targets.
	Specify these values in ddd.ddd.ddd.ddd format.  Multiple IP
	addresses must be separated by a comma.  At least one IP
	address must be given for ARP monitoring to function.  The
	maximum number of targets that can be specified is 16.  The
	default value is no IP addresses.

arp_validate

	Specifies whether or not ARP probes and replies should be
	validated in the active-backup mode.  This causes the ARP
	monitor to examine the incoming ARP requests and replies, and
	only consider a slave to be up if it is receiving the
	appropriate ARP traffic.

	Possible values are:

	none or 0

		No validation is performed.  This is the default.

	active or 1

		Validation is performed only for the active slave.

	backup or 2

		Validation is performed only for backup slaves.

	all or 3

		Validation is performed for all slaves.

	For the active slave, the validation checks ARP replies to
	confirm that they were generated by an arp_ip_target.  Since
	backup slaves do not typically receive these replies, the
	validation performed for backup slaves is on the ARP request
	sent out via the active slave.  It is possible that some
	switch or network configurations may result in situations
	wherein the backup slaves do not receive the ARP requests; in
	such a situation, validation of backup slaves must be
	disabled.

	This option is useful in network configurations in which
	multiple bonding hosts are concurrently issuing ARPs to one or
	more targets beyond a common switch.  Should the link between
	the switch and target fail (but not the switch itself), the
	probe traffic generated by the multiple bonding instances will
	fool the standard ARP monitor into considering the links as
	still up.  Use of the arp_validate option can resolve this, as
	the ARP monitor will only consider ARP requests and replies
	associated with its own instance of bonding.

	This option was added in bonding version 3.1.0.

downdelay

	Specifies the time, in milliseconds, to wait before disabling
	a slave after a link failure has been detected.  This option
	is only valid for the miimon link monitor.  The downdelay
	value should be a multiple of the miimon value; if not, it
	will be rounded down to the nearest multiple.  The default
	value is 0.

fail_over_mac

	Specifies whether active-backup mode should set all slaves to
	the same MAC address at enslavement (the traditional
	behavior), or, when enabled, perform special handling of the
	bond's MAC address in accordance with the selected policy.

	Possible values are:

	none or 0

		This setting disables fail_over_mac, and causes
		bonding to set all slaves of an active-backup bond to
		the same MAC address at enslavement time.  This is the
		default.

	active or 1

		The "active" fail_over_mac policy indicates that the
		MAC address of the bond should always be the MAC
		address of the currently active slave.  The MAC
		address of the slaves is not changed; instead, the MAC
		address of the bond changes during a failover.

		This policy is useful for devices that cannot ever
		alter their MAC address, or for devices that refuse
		incoming broadcasts with their own source MAC (which
		interferes with the ARP monitor).

		The down side of this policy is that every device on
		the network must be updated via gratuitous ARP,
		vs. just updating a switch or set of switches (which
		often takes place for any traffic, not just ARP
		traffic, if the switch snoops incoming traffic to
		update its tables) for the traditional method.  If the
		gratuitous ARP is lost, communication may be
		disrupted.

		When this policy is used in conjunction with the mii
		monitor, devices which assert link up prior to being
		able to actually transmit and receive are particularly
		susceptible to loss of the gratuitous ARP, and an
		appropriate updelay setting may be required.

	follow or 2

		The "follow" fail_over_mac policy causes the MAC
		address of the bond to be selected normally (normally
		the MAC address of the first slave added to the bond).
		However, the second and subsequent slaves are not set
		to this MAC address while they are in a backup role; a
		slave is programmed with the bond's MAC address at
		failover time (and the formerly active slave receives
		the newly active slave's MAC address).

		This policy is useful for multiport devices that
		either become confused or incur a performance penalty
		when multiple ports are programmed with the same MAC
		address.


	The default policy is none, unless the first slave cannot
	change its MAC address, in which case the active policy is
	selected by default.

	This option may be modified via sysfs only when no slaves are
	present in the bond.

	This option was added in bonding version 3.2.0.  The "follow"
	policy was added in bonding version 3.3.0.

lacp_rate

	Option specifying the rate in which we'll ask our link partner
	to transmit LACPDU packets in 802.3ad mode.  Possible values
	are:

	slow or 0
		Request partner to transmit LACPDUs every 30 seconds

	fast or 1
		Request partner to transmit LACPDUs every 1 second

	The default is slow.

max_bonds

	Specifies the number of bonding devices to create for this
	instance of the bonding driver.  E.g., if max_bonds is 3, and
	the bonding driver is not already loaded, then bond0, bond1
	and bond2 will be created.  The default value is 1.  Specifying
	a value of 0 will load bonding, but will not create any devices.

miimon

	Specifies the MII link monitoring frequency in milliseconds.
	This determines how often the link state of each slave is
	inspected for link failures.  A value of zero disables MII
	link monitoring.  A value of 100 is a good starting point.
	The use_carrier option, below, affects how the link state is
	determined.  See the High Availability section for additional
	information.  The default value is 0.

mode

	Specifies one of the bonding policies. The default is
	balance-rr (round robin).  Possible values are:

	balance-rr or 0

		Round-robin policy: Transmit packets in sequential
		order from the first available slave through the
		last.  This mode provides load balancing and fault
		tolerance.

	active-backup or 1

		Active-backup policy: Only one slave in the bond is
		active.  A different slave becomes active if, and only
		if, the active slave fails.  The bond's MAC address is
		externally visible on only one port (network adapter)
		to avoid confusing the switch.

		In bonding version 2.6.2 or later, when a failover
		occurs in active-backup mode, bonding will issue one
		or more gratuitous ARPs on the newly active slave.
		One gratuitous ARP is issued for the bonding master
		interface and each VLAN interfaces configured above
		it, provided that the interface has at least one IP
		address configured.  Gratuitous ARPs issued for VLAN
		interfaces are tagged with the appropriate VLAN id.

		This mode provides fault tolerance.  The primary
		option, documented below, affects the behavior of this
		mode.

	balance-xor or 2

		XOR policy: Transmit based on the selected transmit
		hash policy.  The default policy is a simple [(source
		MAC address XOR'd with destination MAC address) modulo
		slave count].  Alternate transmit policies may be
		selected via the xmit_hash_policy option, described
		below.

		This mode provides load balancing and fault tolerance.

	broadcast or 3

		Broadcast policy: transmits everything on all slave
		interfaces.  This mode provides fault tolerance.

	802.3ad or 4

		IEEE 802.3ad Dynamic link aggregation.  Creates
		aggregation groups that share the same speed and
		duplex settings.  Utilizes all slaves in the active
		aggregator according to the 802.3ad specification.

		Slave selection for outgoing traffic is done according
		to the transmit hash policy, which may be changed from
		the default simple XOR policy via the xmit_hash_policy
		option, documented below.  Note that not all transmit
		policies may be 802.3ad compliant, particularly in
		regards to the packet mis-ordering requirements of
		section 43.2.4 of the 802.3ad standard.  Differing
		peer implementations will have varying tolerances for
		noncompliance.

		Prerequisites:

		1. Ethtool support in the base drivers for retrieving
		the speed and duplex of each slave.

		2. A switch that supports IEEE 802.3ad Dynamic link
		aggregation.

		Most switches will require some type of configuration
		to enable 802.3ad mode.

	balance-tlb or 5

		Adaptive transmit load balancing: channel bonding that
		does not require any special switch support.  The
		outgoing traffic is distributed according to the
		current load (computed relative to the speed) on each
		slave.  Incoming traffic is received by the current
		slave.  If the receiving slave fails, another slave
		takes over the MAC address of the failed receiving
		slave.

		Prerequisite:

		Ethtool support in the base drivers for retrieving the
		speed of each slave.

	balance-alb or 6

		Adaptive load balancing: includes balance-tlb plus
		receive load balancing (rlb) for IPV4 traffic, and
		does not require any special switch support.  The
		receive load balancing is achieved by ARP negotiation.
		The bonding driver intercepts the ARP Replies sent by
		the local system on their way out and overwrites the
		source hardware address with the unique hardware
		address of one of the slaves in the bond such that
		different peers use different hardware addresses for
		the server.

		Receive traffic from connections created by the server
		is also balanced.  When the local system sends an ARP
		Request the bonding driver copies and saves the peer's
		IP information from the ARP packet.  When the ARP
		Reply arrives from the peer, its hardware address is
		retrieved and the bonding driver initiates an ARP
		reply to this peer assigning it to one of the slaves
		in the bond.  A problematic outcome of using ARP
		negotiation for balancing is that each time that an
		ARP request is broadcast it uses the hardware address
		of the bond.  Hence, peers learn the hardware address
		of the bond and the balancing of receive traffic
		collapses to the current slave.  This is handled by
		sending updates (ARP Replies) to all the peers with
		their individually assigned hardware address such that
		the traffic is redistributed.  Receive traffic is also
		redistributed when a new slave is added to the bond
		and when an inactive slave is re-activated.  The
		receive load is distributed sequentially (round robin)
		among the group of highest speed slaves in the bond.

		When a link is reconnected or a new slave joins the
		bond the receive traffic is redistributed among all
		active slaves in the bond by initiating ARP Replies
		with the selected MAC address to each of the
		clients. The updelay parameter (detailed below) must
		be set to a value equal or greater than the switch's
		forwarding delay so that the ARP Replies sent to the
		peers will not be blocked by the switch.

		Prerequisites:

		1. Ethtool support in the base drivers for retrieving
		the speed of each slave.

		2. Base driver support for setting the hardware
		address of a device while it is open.  This is
		required so that there will always be one slave in the
		team using the bond hardware address (the
		curr_active_slave) while having a unique hardware
		address for each slave in the bond.  If the
		curr_active_slave fails its hardware address is
		swapped with the new curr_active_slave that was
		chosen.

num_grat_arp
num_unsol_na

	Specify the number of peer notifications (gratuitous ARPs and
	unsolicited IPv6 Neighbor Advertisements) to be issued after a
	failover event.  As soon as the link is up on the new slave
	(possibly immediately) a peer notification is sent on the
	bonding device and each VLAN sub-device.  This is repeated at
	each link monitor interval (arp_interval or miimon, whichever
	is active) if the number is greater than 1.

	The valid range is 0 - 255; the default value is 1.  These options
	affect only the active-backup mode.  These options were added for
	bonding versions 3.3.0 and 3.4.0 respectively.

	From Linux 2.6.40 and bonding version 3.7.1, these notifications
	are generated by the ipv4 and ipv6 code and the numbers of
	repetitions cannot be set independently.

primary

	A string (eth0, eth2, etc) specifying which slave is the
	primary device.  The specified device will always be the
	active slave while it is available.  Only when the primary is
	off-line will alternate devices be used.  This is useful when
	one slave is preferred over another, e.g., when one slave has
	higher throughput than another.

	The primary option is only valid for active-backup mode.

primary_reselect

	Specifies the reselection policy for the primary slave.  This
	affects how the primary slave is chosen to become the active slave
	when failure of the active slave or recovery of the primary slave
	occurs.  This option is designed to prevent flip-flopping between
	the primary slave and other slaves.  Possible values are:

	always or 0 (default)

		The primary slave becomes the active slave whenever it
		comes back up.

	better or 1

		The primary slave becomes the active slave when it comes
		back up, if the speed and duplex of the primary slave is
		better than the speed and duplex of the current active
		slave.

	failure or 2

		The primary slave becomes the active slave only if the
		current active slave fails and the primary slave is up.

	The primary_reselect setting is ignored in two cases:

		If no slaves are active, the first slave to recover is
		made the active slave.

		When initially enslaved, the primary slave is always made
		the active slave.

	Changing the primary_reselect policy via sysfs will cause an
	immediate selection of the best active slave according to the new
	policy.  This may or may not result in a change of the active
	slave, depending upon the circumstances.

	This option was added for bonding version 3.6.0.

updelay

	Specifies the time, in milliseconds, to wait before enabling a
	slave after a link recovery has been detected.  This option is
	only valid for the miimon link monitor.  The updelay value
	should be a multiple of the miimon value; if not, it will be
	rounded down to the nearest multiple.  The default value is 0.

use_carrier

	Specifies whether or not miimon should use MII or ETHTOOL
	ioctls vs. netif_carrier_ok() to determine the link
	status. The MII or ETHTOOL ioctls are less efficient and
	utilize a deprecated calling sequence within the kernel.  The
	netif_carrier_ok() relies on the device driver to maintain its
	state with netif_carrier_on/off; at this writing, most, but
	not all, device drivers support this facility.

	If bonding insists that the link is up when it should not be,
	it may be that your network device driver does not support
	netif_carrier_on/off.  The default state for netif_carrier is
	"carrier on," so if a driver does not support netif_carrier,
	it will appear as if the link is always up.  In this case,
	setting use_carrier to 0 will cause bonding to revert to the
	MII / ETHTOOL ioctl method to determine the link state.

	A value of 1 enables the use of netif_carrier_ok(), a value of
	0 will use the deprecated MII / ETHTOOL ioctls.  The default
	value is 1.

xmit_hash_policy

	Selects the transmit hash policy to use for slave selection in
	balance-xor and 802.3ad modes.  Possible values are:

	layer2

		Uses XOR of hardware MAC addresses to generate the
		hash.  The formula is

		(source MAC XOR destination MAC) modulo slave count

		This algorithm will place all traffic to a particular
		network peer on the same slave.

		This algorithm is 802.3ad compliant.

	layer2+3

		This policy uses a combination of layer2 and layer3
		protocol information to generate the hash.

		Uses XOR of hardware MAC addresses and IP addresses to
		generate the hash.  The formula is

		(((source IP XOR dest IP) AND 0xffff) XOR
			( source MAC XOR destination MAC ))
				modulo slave count

		This algorithm will place all traffic to a particular
		network peer on the same slave.  For non-IP traffic,
		the formula is the same as for the layer2 transmit
		hash policy.

		This policy is intended to provide a more balanced
		distribution of traffic than layer2 alone, especially
		in environments where a layer3 gateway device is
		required to reach most destinations.

		This algorithm is 802.3ad compliant.

	layer3+4

		This policy uses upper layer protocol information,
		when available, to generate the hash.  This allows for
		traffic to a particular network peer to span multiple
		slaves, although a single connection will not span
		multiple slaves.

		The formula for unfragmented TCP and UDP packets is

		((source port XOR dest port) XOR
			 ((source IP XOR dest IP) AND 0xffff)
				modulo slave count

		For fragmented TCP or UDP packets and all other IP
		protocol traffic, the source and destination port
		information is omitted.  For non-IP traffic, the
		formula is the same as for the layer2 transmit hash
		policy.

		This policy is intended to mimic the behavior of
		certain switches, notably Cisco switches with PFC2 as
		well as some Foundry and IBM products.

		This algorithm is not fully 802.3ad compliant.  A
		single TCP or UDP conversation containing both
		fragmented and unfragmented packets will see packets
		striped across two interfaces.  This may result in out
		of order delivery.  Most traffic types will not meet
		this criteria, as TCP rarely fragments traffic, and
		most UDP traffic is not involved in extended
		conversations.  Other implementations of 802.3ad may
		or may not tolerate this noncompliance.

	The default value is layer2.  This option was added in bonding
	version 2.6.3.  In earlier versions of bonding, this parameter
	does not exist, and the layer2 policy is the only policy.  The
	layer2+3 value was added for bonding version 3.2.2.

resend_igmp

	Specifies the number of IGMP membership reports to be issued after
	a failover event. One membership report is issued immediately after
	the failover, subsequent packets are sent in each 200ms interval.

	The valid range is 0 - 255; the default value is 1. A value of 0
	prevents the IGMP membership report from being issued in response
	to the failover event.

	This option is useful for bonding modes balance-rr (0), active-backup
	(1), balance-tlb (5) and balance-alb (6), in which a failover can
	switch the IGMP traffic from one slave to another.  Therefore a fresh
	IGMP report must be issued to cause the switch to forward the incoming
	IGMP traffic over the newly selected slave.

	This option was added for bonding version 3.7.0.

3. Configuring Bonding Devices
==============================

	You can configure bonding using either your distro's network
initialization scripts, or manually using either ifenslave or the
sysfs interface.  Distros generally use one of three packages for the
network initialization scripts: initscripts, sysconfig or interfaces.
Recent versions of these packages have support for bonding, while older
versions do not.

	We will first describe the options for configuring bonding for
distros using versions of initscripts, sysconfig and interfaces with full
or partial support for bonding, then provide information on enabling
bonding without support from the network initialization scripts (i.e.,
older versions of initscripts or sysconfig).

	If you're unsure whether your distro uses sysconfig,
initscripts or interfaces, or don't know if it's new enough, have no fear.
Determining this is fairly straightforward.

	First, look for a file called interfaces in /etc/network directory.
If this file is present in your system, then your system use interfaces. See
Configuration with Interfaces Support.

	Else, issue the command:

$ rpm -qf /sbin/ifup

	It will respond with a line of text starting with either
"initscripts" or "sysconfig," followed by some numbers.  This is the
package that provides your network initialization scripts.

	Next, to determine if your installation supports bonding,
issue the command:

$ grep ifenslave /sbin/ifup

	If this returns any matches, then your initscripts or
sysconfig has support for bonding.

3.1 Configuration with Sysconfig Support
----------------------------------------

	This section applies to distros using a version of sysconfig
with bonding support, for example, SuSE Linux Enterprise Server 9.

	SuSE SLES 9's networking configuration system does support
bonding, however, at this writing, the YaST system configuration
front end does not provide any means to work with bonding devices.
Bonding devices can be managed by hand, however, as follows.

	First, if they have not already been configured, configure the
slave devices.  On SLES 9, this is most easily done by running the
yast2 sysconfig configuration utility.  The goal is for to create an
ifcfg-id file for each slave device.  The simplest way to accomplish
this is to configure the devices for DHCP (this is only to get the
file ifcfg-id file created; see below for some issues with DHCP).  The
name of the configuration file for each device will be of the form:

ifcfg-id-xx:xx:xx:xx:xx:xx

	Where the "xx" portion will be replaced with the digits from
the device's permanent MAC address.

	Once the set of ifcfg-id-xx:xx:xx:xx:xx:xx files has been
created, it is necessary to edit the configuration files for the slave
devices (the MAC addresses correspond to those of the slave devices).
Before editing, the file will contain multiple lines, and will look
something like this:

BOOTPROTO='dhcp'
STARTMODE='on'
USERCTL='no'
UNIQUE='XNzu.WeZGOGF+4wE'
_nm_name='bus-pci-0001:61:01.0'

	Change the BOOTPROTO and STARTMODE lines to the following:

BOOTPROTO='none'
STARTMODE='off'

	Do not alter the UNIQUE or _nm_name lines.  Remove any other
lines (USERCTL, etc).

	Once the ifcfg-id-xx:xx:xx:xx:xx:xx files have been modified,
it's time to create the configuration file for the bonding device
itself.  This file is named ifcfg-bondX, where X is the number of the
bonding device to create, starting at 0.  The first such file is
ifcfg-bond0, the second is ifcfg-bond1, and so on.  The sysconfig
network configuration system will correctly start multiple instances
of bonding.

	The contents of the ifcfg-bondX file is as follows:

BOOTPROTO="static"
BROADCAST="10.0.2.255"
IPADDR="10.0.2.10"
NETMASK="255.255.0.0"
NETWORK="10.0.2.0"
REMOTE_IPADDR=""
STARTMODE="onboot"
BONDING_MASTER="yes"
BONDING_MODULE_OPTS="mode=active-backup miimon=100"
BONDING_SLAVE0="eth0"
BONDING_SLAVE1="bus-pci-0000:06:08.1"

	Replace the sample BROADCAST, IPADDR, NETMASK and NETWORK
values with the appropriate values for your network.

	The STARTMODE specifies when the device is brought online.
The possible values are:

	onboot:	 The device is started at boot time.  If you're not
		 sure, this is probably what you want.

	manual:	 The device is started only when ifup is called
		 manually.  Bonding devices may be configured this
		 way if you do not wish them to start automatically
		 at boot for some reason.

	hotplug: The device is started by a hotplug event.  This is not
		 a valid choice for a bonding device.

	off or ignore: The device configuration is ignored.

	The line BONDING_MASTER='yes' indicates that the device is a
bonding master device.  The only useful value is "yes."

	The contents of BONDING_MODULE_OPTS are supplied to the
instance of the bonding module for this device.  Specify the options
for the bonding mode, link monitoring, and so on here.  Do not include
the max_bonds bonding parameter; this will confuse the configuration
system if you have multiple bonding devices.

	Finally, supply one BONDING_SLAVEn="slave device" for each
slave.  where "n" is an increasing value, one for each slave.  The
"slave device" is either an interface name, e.g., "eth0", or a device
specifier for the network device.  The interface name is easier to
find, but the ethN names are subject to change at boot time if, e.g.,
a device early in the sequence has failed.  The device specifiers
(bus-pci-0000:06:08.1 in the example above) specify the physical
network device, and will not change unless the device's bus location
changes (for example, it is moved from one PCI slot to another).  The
example above uses one of each type for demonstration purposes; most
configurations will choose one or the other for all slave devices.

	When all configuration files have been modified or created,
networking must be restarted for the configuration changes to take
effect.  This can be accomplished via the following:

# /etc/init.d/network restart

	Note that the network control script (/sbin/ifdown) will
remove the bonding module as part of the network shutdown processing,
so it is not necessary to remove the module by hand if, e.g., the
module parameters have changed.

	Also, at this writing, YaST/YaST2 will not manage bonding
devices (they do not show bonding interfaces on its list of network
devices).  It is necessary to edit the configuration file by hand to
change the bonding configuration.

	Additional general options and details of the ifcfg file
format can be found in an example ifcfg template file:

/etc/sysconfig/network/ifcfg.template

	Note that the template does not document the various BONDING_
settings described above, but does describe many of the other options.

3.1.1 Using DHCP with Sysconfig
-------------------------------

	Under sysconfig, configuring a device with BOOTPROTO='dhcp'
will cause it to query DHCP for its IP address information.  At this
writing, this does not function for bonding devices; the scripts
attempt to obtain the device address from DHCP prior to adding any of
the slave devices.  Without active slaves, the DHCP requests are not
sent to the network.

3.1.2 Configuring Multiple Bonds with Sysconfig
-----------------------------------------------

	The sysconfig network initialization system is capable of
handling multiple bonding devices.  All that is necessary is for each
bonding instance to have an appropriately configured ifcfg-bondX file
(as described above).  Do not specify the "max_bonds" parameter to any
instance of bonding, as this will confuse sysconfig.  If you require
multiple bonding devices with identical parameters, create multiple
ifcfg-bondX files.

	Because the sysconfig scripts supply the bonding module
options in the ifcfg-bondX file, it is not necessary to add them to
the system /etc/modules.conf or /etc/modprobe.conf configuration file.

3.2 Configuration with Initscripts Support
------------------------------------------

	This section applies to distros using a recent version of
initscripts with bonding support, for example, Red Hat Enterprise Linux
version 3 or later, Fedora, etc.  On these systems, the network
initialization scripts have knowledge of bonding, and can be configured to
control bonding devices.  Note that older versions of the initscripts
package have lower levels of support for bonding; this will be noted where
applicable.

	These distros will not automatically load the network adapter
driver unless the ethX device is configured with an IP address.
Because of this constraint, users must manually configure a
network-script file for all physical adapters that will be members of
a bondX link.  Network script files are located in the directory:

/etc/sysconfig/network-scripts

	The file name must be prefixed with "ifcfg-eth" and suffixed
with the adapter's physical adapter number.  For example, the script
for eth0 would be named /etc/sysconfig/network-scripts/ifcfg-eth0.
Place the following text in the file:

DEVICE=eth0
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none

	The DEVICE= line will be different for every ethX device and
must correspond with the name of the file, i.e., ifcfg-eth1 must have
a device line of DEVICE=eth1.  The setting of the MASTER= line will
also depend on the final bonding interface name chosen for your bond.
As with other network devices, these typically start at 0, and go up
one for each device, i.e., the first bonding instance is bond0, the
second is bond1, and so on.

	Next, create a bond network script.  The file name for this
script will be /etc/sysconfig/network-scripts/ifcfg-bondX where X is
the number of the bond.  For bond0 the file is named "ifcfg-bond0",
for bond1 it is named "ifcfg-bond1", and so on.  Within that file,
place the following text:

DEVICE=bond0
IPADDR=192.168.1.1
NETMASK=255.255.255.0
NETWORK=192.168.1.0
BROADCAST=192.168.1.255
ONBOOT=yes
BOOTPROTO=none
USERCTL=no

	Be sure to change the networking specific lines (IPADDR,
NETMASK, NETWORK and BROADCAST) to match your network configuration.

	For later versions of initscripts, such as that found with Fedora
7 (or later) and Red Hat Enterprise Linux version 5 (or later), it is possible,
and, indeed, preferable, to specify the bonding options in the ifcfg-bond0
file, e.g. a line of the format:

BONDING_OPTS="mode=active-backup arp_interval=60 arp_ip_target=192.168.1.254"

	will configure the bond with the specified options.  The options
specified in BONDING_OPTS are identical to the bonding module parameters
except for the arp_ip_target field when using versions of initscripts older
than and 8.57 (Fedora 8) and 8.45.19 (Red Hat Enterprise Linux 5.2).  When
using older versions each target should be included as a separate option and
should be preceded by a '+' to indicate it should be added to the list of
queried targets, e.g.,

	arp_ip_target=+192.168.1.1 arp_ip_target=+192.168.1.2

	is the proper syntax to specify multiple targets.  When specifying
options via BONDING_OPTS, it is not necessary to edit /etc/modules.conf or
/etc/modprobe.conf.

	For even older versions of initscripts that do not support
BONDING_OPTS, it is necessary to edit /etc/modules.conf (or
/etc/modprobe.conf, depending upon your distro) to load the bonding module
with your desired options when the bond0 interface is brought up.  The
following lines in /etc/modules.conf (or modprobe.conf) will load the
bonding module, and select its options:

alias bond0 bonding
options bond0 mode=balance-alb miimon=100

	Replace the sample parameters with the appropriate set of
options for your configuration.

	Finally run "/etc/rc.d/init.d/network restart" as root.  This
will restart the networking subsystem and your bond link should be now
up and running.

3.2.1 Using DHCP with Initscripts
---------------------------------

	Recent versions of initscripts (the versions supplied with Fedora
Core 3 and Red Hat Enterprise Linux 4, or later versions, are reported to
work) have support for assigning IP information to bonding devices via
DHCP.

	To configure bonding for DHCP, configure it as described
above, except replace the line "BOOTPROTO=none" with "BOOTPROTO=dhcp"
and add a line consisting of "TYPE=Bonding".  Note that the TYPE value
is case sensitive.

3.2.2 Configuring Multiple Bonds with Initscripts
-------------------------------------------------

	Initscripts packages that are included with Fedora 7 and Red Hat
Enterprise Linux 5 support multiple bonding interfaces by simply
specifying the appropriate BONDING_OPTS= in ifcfg-bondX where X is the
number of the bond.  This support requires sysfs support in the kernel,
and a bonding driver of version 3.0.0 or later.  Other configurations may
not support this method for specifying multiple bonding interfaces; for
those instances, see the "Configuring Multiple Bonds Manually" section,
below.

3.3 Configuring Bonding Manually with Ifenslave
-----------------------------------------------

	This section applies to distros whose network initialization
scripts (the sysconfig or initscripts package) do not have specific
knowledge of bonding.  One such distro is SuSE Linux Enterprise Server
version 8.

	The general method for these systems is to place the bonding
module parameters into /etc/modules.conf or /etc/modprobe.conf (as
appropriate for the installed distro), then add modprobe and/or
ifenslave commands to the system's global init script.  The name of
the global init script differs; for sysconfig, it is
/etc/init.d/boot.local and for initscripts it is /etc/rc.d/rc.local.

	For example, if you wanted to make a simple bond of two e100
devices (presumed to be eth0 and eth1), and have it persist across
reboots, edit the appropriate file (/etc/init.d/boot.local or
/etc/rc.d/rc.local), and add the following:

modprobe bonding mode=balance-alb miimon=100
modprobe e100
ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
ifenslave bond0 eth0
ifenslave bond0 eth1

	Replace the example bonding module parameters and bond0
network configuration (IP address, netmask, etc) with the appropriate
values for your configuration.

	Unfortunately, this method will not provide support for the
ifup and ifdown scripts on the bond devices.  To reload the bonding
configuration, it is necessary to run the initialization script, e.g.,

# /etc/init.d/boot.local

	or

# /etc/rc.d/rc.local

	It may be desirable in such a case to create a separate script
which only initializes the bonding configuration, then call that
separate script from within boot.local.  This allows for bonding to be
enabled without re-running the entire global init script.

	To shut down the bonding devices, it is necessary to first
mark the bonding device itself as being down, then remove the
appropriate device driver modules.  For our example above, you can do
the following:

# ifconfig bond0 down
# rmmod bonding
# rmmod e100

	Again, for convenience, it may be desirable to create a script
with these commands.


3.3.1 Configuring Multiple Bonds Manually
-----------------------------------------

	This section contains information on configuring multiple
bonding devices with differing options for those systems whose network
initialization scripts lack support for configuring multiple bonds.

	If you require multiple bonding devices, but all with the same
options, you may wish to use the "max_bonds" module parameter,
documented above.

	To create multiple bonding devices with differing options, it is
preferrable to use bonding parameters exported by sysfs, documented in the
section below.

	For versions of bonding without sysfs support, the only means to
provide multiple instances of bonding with differing options is to load
the bonding driver multiple times.  Note that current versions of the
sysconfig network initialization scripts handle this automatically; if
your distro uses these scripts, no special action is needed.  See the
section Configuring Bonding Devices, above, if you're not sure about your
network initialization scripts.

	To load multiple instances of the module, it is necessary to
specify a different name for each instance (the module loading system
requires that every loaded module, even multiple instances of the same
module, have a unique name).  This is accomplished by supplying multiple
sets of bonding options in /etc/modprobe.conf, for example:

alias bond0 bonding
options bond0 -o bond0 mode=balance-rr miimon=100

alias bond1 bonding
options bond1 -o bond1 mode=balance-alb miimon=50

	will load the bonding module two times.  The first instance is
named "bond0" and creates the bond0 device in balance-rr mode with an
miimon of 100.  The second instance is named "bond1" and creates the
bond1 device in balance-alb mode with an miimon of 50.

	In some circumstances (typically with older distributions),
the above does not work, and the second bonding instance never sees
its options.  In that case, the second options line can be substituted
as follows:

install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
	mode=balance-alb miimon=50

	This may be repeated any number of times, specifying a new and
unique name in place of bond1 for each subsequent instance.

	It has been observed that some Red Hat supplied kernels are unable
to rename modules at load time (the "-o bond1" part).  Attempts to pass
that option to modprobe will produce an "Operation not permitted" error.
This has been reported on some Fedora Core kernels, and has been seen on
RHEL 4 as well.  On kernels exhibiting this problem, it will be impossible
to configure multiple bonds with differing parameters (as they are older
kernels, and also lack sysfs support).

3.4 Configuring Bonding Manually via Sysfs
------------------------------------------

	Starting with version 3.0.0, Channel Bonding may be configured
via the sysfs interface.  This interface allows dynamic configuration
of all bonds in the system without unloading the module.  It also
allows for adding and removing bonds at runtime.  Ifenslave is no
longer required, though it is still supported.

	Use of the sysfs interface allows you to use multiple bonds
with different configurations without having to reload the module.
It also allows you to use multiple, differently configured bonds when
bonding is compiled into the kernel.

	You must have the sysfs filesystem mounted to configure
bonding this way.  The examples in this document assume that you
are using the standard mount point for sysfs, e.g. /sys.  If your
sysfs filesystem is mounted elsewhere, you will need to adjust the
example paths accordingly.

Creating and Destroying Bonds
-----------------------------
To add a new bond foo:
# echo +foo > /sys/class/net/bonding_masters

To remove an existing bond bar:
# echo -bar > /sys/class/net/bonding_masters

To show all existing bonds:
# cat /sys/class/net/bonding_masters

NOTE: due to 4K size limitation of sysfs files, this list may be
truncated if you have more than a few hundred bonds.  This is unlikely
to occur under normal operating conditions.

Adding and Removing Slaves
--------------------------
	Interfaces may be enslaved to a bond using the file
/sys/class/net//bonding/slaves.  The semantics for this file
are the same as for the bonding_masters file.

To enslave interface eth0 to bond bond0:
# ifconfig bond0 up
# echo +eth0 > /sys/class/net/bond0/bonding/slaves

To free slave eth0 from bond bond0:
# echo -eth0 > /sys/class/net/bond0/bonding/slaves

	When an interface is enslaved to a bond, symlinks between the
two are created in the sysfs filesystem.  In this case, you would get
/sys/class/net/bond0/slave_eth0 pointing to /sys/class/net/eth0, and
/sys/class/net/eth0/master pointing to /sys/class/net/bond0.

	This means that you can tell quickly whether or not an
interface is enslaved by looking for the master symlink.  Thus:
# echo -eth0 > /sys/class/net/eth0/master/bonding/slaves
will free eth0 from whatever bond it is enslaved to, regardless of
the name of the bond interface.

Changing a Bond's Configuration
-------------------------------
	Each bond may be configured individually by manipulating the
files located in /sys/class/net//bonding

	The names of these files correspond directly with the command-
line parameters described elsewhere in this file, and, with the
exception of arp_ip_target, they accept the same values.  To see the
current setting, simply cat the appropriate file.

	A few examples will be given here; for specific usage
guidelines for each parameter, see the appropriate section in this
document.

To configure bond0 for balance-alb mode:
# ifconfig bond0 down
# echo 6 > /sys/class/net/bond0/bonding/mode
 - or -
# echo balance-alb > /sys/class/net/bond0/bonding/mode
	NOTE: The bond interface must be down before the mode can be
changed.

To enable MII monitoring on bond0 with a 1 second interval:
# echo 1000 > /sys/class/net/bond0/bonding/miimon
	NOTE: If ARP monitoring is enabled, it will disabled when MII
monitoring is enabled, and vice-versa.

To add ARP targets:
# echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target
# echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target
	NOTE:  up to 16 target addresses may be specified.

To remove an ARP target:
# echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target

Example Configuration
---------------------
	We begin with the same example that is shown in section 3.3,
executed with sysfs, and without using ifenslave.

	To make a simple bond of two e100 devices (presumed to be eth0
and eth1), and have it persist across reboots, edit the appropriate
file (/etc/init.d/boot.local or /etc/rc.d/rc.local), and add the
following:

modprobe bonding
modprobe e100
echo balance-alb > /sys/class/net/bond0/bonding/mode
ifconfig bond0 192.168.1.1 netmask 255.255.255.0 up
echo 100 > /sys/class/net/bond0/bonding/miimon
echo +eth0 > /sys/class/net/bond0/bonding/slaves
echo +eth1 > /sys/class/net/bond0/bonding/slaves

	To add a second bond, with two e1000 interfaces in
active-backup mode, using ARP monitoring, add the following lines to
your init script:

modprobe e1000
echo +bond1 > /sys/class/net/bonding_masters
echo active-backup > /sys/class/net/bond1/bonding/mode
ifconfig bond1 192.168.2.1 netmask 255.255.255.0 up
echo +192.168.2.100 /sys/class/net/bond1/bonding/arp_ip_target
echo 2000 > /sys/class/net/bond1/bonding/arp_interval
echo +eth2 > /sys/class/net/bond1/bonding/slaves
echo +eth3 > /sys/class/net/bond1/bonding/slaves

3.5 Configuration with Interfaces Support
-----------------------------------------

        This section applies to distros which use /etc/network/interfaces file
to describe network interface configuration, most notably Debian and it's
derivatives.

	The ifup and ifdown commands on Debian don't support bonding out of
the box. The ifenslave-2.6 package should be installed to provide bonding
support.  Once installed, this package will provide bond-* options to be used
into /etc/network/interfaces.

	Note that ifenslave-2.6 package will load the bonding module and use
the ifenslave command when appropriate.

Example Configurations
----------------------

In /etc/network/interfaces, the following stanza will configure bond0, in
active-backup mode, with eth0 and eth1 as slaves.

auto bond0
iface bond0 inet dhcp
	bond-slaves eth0 eth1
	bond-mode active-backup
	bond-miimon 100
	bond-primary eth0 eth1

If the above configuration doesn't work, you might have a system using
upstart for system startup. This is most notably true for recent
Ubuntu versions. The following stanza in /etc/network/interfaces will
produce the same result on those systems.

auto bond0
iface bond0 inet dhcp
	bond-slaves none
	bond-mode active-backup
	bond-miimon 100

auto eth0
iface eth0 inet manual
	bond-master bond0
	bond-primary eth0 eth1

auto eth1
iface eth1 inet manual
	bond-master bond0
	bond-primary eth0 eth1

For a full list of bond-* supported options in /etc/network/interfaces and some
more advanced examples tailored to you particular distros, see the files in
/usr/share/doc/ifenslave-2.6.

3.6 Overriding Configuration for Special Cases
----------------------------------------------

When using the bonding driver, the physical port which transmits a frame is
typically selected by the bonding driver, and is not relevant to the user or
system administrator.  The output port is simply selected using the policies of
the selected bonding mode.  On occasion however, it is helpful to direct certain
classes of traffic to certain physical interfaces on output to implement
slightly more complex policies.  For example, to reach a web server over a
bonded interface in which eth0 connects to a private network, while eth1
connects via a public network, it may be desirous to bias the bond to send said
traffic over eth0 first, using eth1 only as a fall back, while all other traffic
can safely be sent over either interface.  Such configurations may be achieved
using the traffic control utilities inherent in linux.

By default the bonding driver is multiqueue aware and 16 queues are created
when the driver initializes (see Documentation/networking/multiqueue.txt
for details).  If more or less queues are desired the module parameter
tx_queues can be used to change this value.  There is no sysfs parameter
available as the allocation is done at module init time.

The output of the file /proc/net/bonding/bondX has changed so the output Queue
ID is now printed for each slave:

Bonding Mode: fault-tolerance (active-backup)
Primary Slave: None
Currently Active Slave: eth0
MII Status: up
MII Polling Interval (ms): 0
Up Delay (ms): 0
Down Delay (ms): 0

Slave Interface: eth0
MII Status: up
Link Failure Count: 0
Permanent HW addr: 00:1a:a0:12:8f:cb
Slave queue ID: 0

Slave Interface: eth1
MII Status: up
Link Failure Count: 0
Permanent HW addr: 00:1a:a0:12:8f:cc
Slave queue ID: 2

The queue_id for a slave can be set using the command:

# echo "eth1:2" > /sys/class/net/bond0/bonding/queue_id

Any interface that needs a queue_id set should set it with multiple calls
like the one above until proper priorities are set for all interfaces.  On
distributions that allow configuration via initscripts, multiple 'queue_id'
arguments can be added to BONDING_OPTS to set all needed slave queues.

These queue id's can be used in conjunction with the tc utility to configure
a multiqueue qdisc and filters to bias certain traffic to transmit on certain
slave devices.  For instance, say we wanted, in the above configuration to
force all traffic bound to 192.168.1.100 to use eth1 in the bond as its output
device. The following commands would accomplish this:

# tc qdisc add dev bond0 handle 1 root multiq

# tc filter add dev bond0 protocol ip parent 1: prio 1 u32 match ip dst \
	192.168.1.100 action skbedit queue_mapping 2

These commands tell the kernel to attach a multiqueue queue discipline to the
bond0 interface and filter traffic enqueued to it, such that packets with a dst
ip of 192.168.1.100 have their output queue mapping value overwritten to 2.
This value is then passed into the driver, causing the normal output path
selection policy to be overridden, selecting instead qid 2, which maps to eth1.

Note that qid values begin at 1.  Qid 0 is reserved to initiate to the driver
that normal output policy selection should take place.  One benefit to simply
leaving the qid for a slave to 0 is the multiqueue awareness in the bonding
driver that is now present.  This awareness allows tc filters to be placed on
slave devices as well as bond devices and the bonding driver will simply act as
a pass-through for selecting output queues on the slave device rather than 
output port selection.

This feature first appeared in bonding driver version 3.7.0 and support for
output slave selection was limited to round-robin and active-backup modes.

4 Querying Bonding Configuration
=================================

4.1 Bonding Configuration
-------------------------

	Each bonding device has a read-only file residing in the
/proc/net/bonding directory.  The file contents include information
about the bonding configuration, options and state of each slave.

	For example, the contents of /proc/net/bonding/bond0 after the
driver is loaded with parameters of mode=0 and miimon=1000 is
generally as follows:

	Ethernet Channel Bonding Driver: 2.6.1 (October 29, 2004)
        Bonding Mode: load balancing (round-robin)
        Currently Active Slave: eth0
        MII Status: up
        MII Polling Interval (ms): 1000
        Up Delay (ms): 0
        Down Delay (ms): 0

        Slave Interface: eth1
        MII Status: up
        Link Failure Count: 1

        Slave Interface: eth0
        MII Status: up
        Link Failure Count: 1

	The precise format and contents will change depending upon the
bonding configuration, state, and version of the bonding driver.

4.2 Network configuration
-------------------------

	The network configuration can be inspected using the ifconfig
command.  Bonding devices will have the MASTER flag set; Bonding slave
devices will have the SLAVE flag set.  The ifconfig output does not
contain information on which slaves are associated with which masters.

	In the example below, the bond0 interface is the master
(MASTER) while eth0 and eth1 are slaves (SLAVE). Notice all slaves of
bond0 have the same MAC address (HWaddr) as bond0 for all modes except
TLB and ALB that require a unique MAC address for each slave.

# /sbin/ifconfig
bond0     Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
          inet addr:XXX.XXX.XXX.YYY  Bcast:XXX.XXX.XXX.255  Mask:255.255.252.0
          UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1
          RX packets:7224794 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3286647 errors:1 dropped:0 overruns:1 carrier:0
          collisions:0 txqueuelen:0

eth0      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
          UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
          RX packets:3573025 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1643167 errors:1 dropped:0 overruns:1 carrier:0
          collisions:0 txqueuelen:100
          Interrupt:10 Base address:0x1080

eth1      Link encap:Ethernet  HWaddr 00:C0:F0:1F:37:B4
          UP BROADCAST RUNNING SLAVE MULTICAST  MTU:1500  Metric:1
          RX packets:3651769 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1643480 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          Interrupt:9 Base address:0x1400

5. Switch Configuration
=======================

	For this section, "switch" refers to whatever system the
bonded devices are directly connected to (i.e., where the other end of
the cable plugs into).  This may be an actual dedicated switch device,
or it may be another regular system (e.g., another computer running
Linux),

	The active-backup, balance-tlb and balance-alb modes do not
require any specific configuration of the switch.

	The 802.3ad mode requires that the switch have the appropriate
ports configured as an 802.3ad aggregation.  The precise method used
to configure this varies from switch to switch, but, for example, a
Cisco 3550 series switch requires that the appropriate ports first be
grouped together in a single etherchannel instance, then that
etherchannel is set to mode "lacp" to enable 802.3ad (instead of
standard EtherChannel).

	The balance-rr, balance-xor and broadcast modes generally
require that the switch have the appropriate ports grouped together.
The nomenclature for such a group differs between switches, it may be
called an "etherchannel" (as in the Cisco example, above), a "trunk
group" or some other similar variation.  For these modes, each switch
will also have its own configuration options for the switch's transmit
policy to the bond.  Typical choices include XOR of either the MAC or
IP addresses.  The transmit policy of the two peers does not need to
match.  For these three modes, the bonding mode really selects a
transmit policy for an EtherChannel group; all three will interoperate
with another EtherChannel group.


6. 802.1q VLAN Support
======================

	It is possible to configure VLAN devices over a bond interface
using the 8021q driver.  However, only packets coming from the 8021q
driver and passing through bonding will be tagged by default.  Self
generated packets, for example, bonding's learning packets or ARP
packets generated by either ALB mode or the ARP monitor mechanism, are
tagged internally by bonding itself.  As a result, bonding must
"learn" the VLAN IDs configured above it, and use those IDs to tag
self generated packets.

	For reasons of simplicity, and to support the use of adapters
that can do VLAN hardware acceleration offloading, the bonding
interface declares itself as fully hardware offloading capable, it gets
the add_vid/kill_vid notifications to gather the necessary
information, and it propagates those actions to the slaves.  In case
of mixed adapter types, hardware accelerated tagged packets that
should go through an adapter that is not offloading capable are
"un-accelerated" by the bonding driver so the VLAN tag sits in the
regular location.

	VLAN interfaces *must* be added on top of a bonding interface
only after enslaving at least one slave.  The bonding interface has a
hardware address of 00:00:00:00:00:00 until the first slave is added.
If the VLAN interface is created prior to the first enslavement, it
would pick up the all-zeroes hardware address.  Once the first slave
is attached to the bond, the bond device itself will pick up the
slave's hardware address, which is then available for the VLAN device.

	Also, be aware that a similar problem can occur if all slaves
are released from a bond that still has one or more VLAN interfaces on
top of it.  When a new slave is added, the bonding interface will
obtain its hardware address from the first slave, which might not
match the hardware address of the VLAN interfaces (which was
ultimately copied from an earlier slave).

	There are two methods to insure that the VLAN device operates
with the correct hardware address if all slaves are removed from a
bond interface:

	1. Remove all VLAN interfaces then recreate them

	2. Set the bonding interface's hardware address so that it
matches the hardware address of the VLAN interfaces.

	Note that changing a VLAN interface's HW address would set the
underlying device -- i.e. the bonding interface -- to promiscuous
mode, which might not be what you want.


7. Link Monitoring
==================

	The bonding driver at present supports two schemes for
monitoring a slave device's link state: the ARP monitor and the MII
monitor.

	At the present time, due to implementation restrictions in the
bonding driver itself, it is not possible to enable both ARP and MII
monitoring simultaneously.

7.1 ARP Monitor Operation
-------------------------

	The ARP monitor operates as its name suggests: it sends ARP
queries to one or more designated peer systems on the network, and
uses the response as an indication that the link is operating.  This
gives some assurance that traffic is actually flowing to and from one
or more peers on the local network.

	The ARP monitor relies on the device driver itself to verify
that traffic is flowing.  In particular, the driver must keep up to
date the last receive time, dev->last_rx, and transmit start time,
dev->trans_start.  If these are not updated by the driver, then the
ARP monitor will immediately fail any slaves using that driver, and
those slaves will stay down.  If networking monitoring (tcpdump, etc)
shows the ARP requests and replies on the network, then it may be that
your device driver is not updating last_rx and trans_start.

7.2 Configuring Multiple ARP Targets
------------------------------------

	While ARP monitoring can be done with just one target, it can
be useful in a High Availability setup to have several targets to
monitor.  In the case of just one target, the target itself may go
down or have a problem making it unresponsive to ARP requests.  Having
an additional target (or several) increases the reliability of the ARP
monitoring.

	Multiple ARP targets must be separated by commas as follows:

# example options for ARP monitoring with three targets
alias bond0 bonding
options bond0 arp_interval=60 arp_ip_target=192.168.0.1,192.168.0.3,192.168.0.9

	For just a single target the options would resemble:

# example options for ARP monitoring with one target
alias bond0 bonding
options bond0 arp_interval=60 arp_ip_target=192.168.0.100


7.3 MII Monitor Operation
-------------------------

	The MII monitor monitors only the carrier state of the local
network interface.  It accomplishes this in one of three ways: by
depending upon the device driver to maintain its carrier state, by
querying the device's MII registers, or by making an ethtool query to
the device.

	If the use_carrier module parameter is 1 (the default value),
then the MII monitor will rely on the driver for carrier state
information (via the netif_carrier subsystem).  As explained in the
use_carrier parameter information, above, if the MII monitor fails to
detect carrier loss on the device (e.g., when the cable is physically
disconnected), it may be that the driver does not support
netif_carrier.

	If use_carrier is 0, then the MII monitor will first query the
device's (via ioctl) MII registers and check the link state.  If that
request fails (not just that it returns carrier down), then the MII
monitor will make an ethtool ETHOOL_GLINK request to attempt to obtain
the same information.  If both methods fail (i.e., the driver either
does not support or had some error in processing both the MII register
and ethtool requests), then the MII monitor will assume the link is
up.

8. Potential Sources of Trouble
===============================

8.1 Adventures in Routing
-------------------------

	When bonding is configured, it is important that the slave
devices not have routes that supersede routes of the master (or,
generally, not have routes at all).  For example, suppose the bonding
device bond0 has two slaves, eth0 and eth1, and the routing table is
as follows:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth0
10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 eth1
10.0.0.0        0.0.0.0         255.255.0.0     U        40 0          0 bond0
127.0.0.0       0.0.0.0         255.0.0.0       U        40 0          0 lo

	This routing configuration will likely still update the
receive/transmit times in the driver (needed by the ARP monitor), but
may bypass the bonding driver (because outgoing traffic to, in this
case, another host on network 10 would use eth0 or eth1 before bond0).

	The ARP monitor (and ARP itself) may become confused by this
configuration, because ARP requests (generated by the ARP monitor)
will be sent on one interface (bond0), but the corresponding reply
will arrive on a different interface (eth0).  This reply looks to ARP
as an unsolicited ARP reply (because ARP matches replies on an
interface basis), and is discarded.  The MII monitor is not affected
by the state of the routing table.

	The solution here is simply to insure that slaves do not have
routes of their own, and if for some reason they must, those routes do
not supersede routes of their master.  This should generally be the
case, but unusual configurations or errant manual or automatic static
route additions may cause trouble.

8.2 Ethernet Device Renaming
----------------------------

	On systems with network configuration scripts that do not
associate physical devices directly with network interface names (so
that the same physical device always has the same "ethX" name), it may
be necessary to add some special logic to either /etc/modules.conf or
/etc/modprobe.conf (depending upon which is installed on the system).

	For example, given a modules.conf containing the following:

alias bond0 bonding
options bond0 mode=some-mode miimon=50
alias eth0 tg3
alias eth1 tg3
alias eth2 e1000
alias eth3 e1000

	If neither eth0 and eth1 are slaves to bond0, then when the
bond0 interface comes up, the devices may end up reordered.  This
happens because bonding is loaded first, then its slave device's
drivers are loaded next.  Since no other drivers have been loaded,
when the e1000 driver loads, it will receive eth0 and eth1 for its
devices, but the bonding configuration tries to enslave eth2 and eth3
(which may later be assigned to the tg3 devices).

	Adding the following:

add above bonding e1000 tg3

	causes modprobe to load e1000 then tg3, in that order, when
bonding is loaded.  This command is fully documented in the
modules.conf manual page.

	On systems utilizing modprobe.conf (or modprobe.conf.local),
an equivalent problem can occur.  In this case, the following can be
added to modprobe.conf (or modprobe.conf.local, as appropriate), as
follows (all on one line; it has been split here for clarity):

install bonding /sbin/modprobe tg3; /sbin/modprobe e1000;
	/sbin/modprobe --ignore-install bonding

	This will, when loading the bonding module, rather than
performing the normal action, instead execute the provided command.
This command loads the device drivers in the order needed, then calls
modprobe with --ignore-install to cause the normal action to then take
place.  Full documentation on this can be found in the modprobe.conf
and modprobe manual pages.

8.3. Painfully Slow Or No Failed Link Detection By Miimon
---------------------------------------------------------

	By default, bonding enables the use_carrier option, which
instructs bonding to trust the driver to maintain carrier state.

	As discussed in the options section, above, some drivers do
not support the netif_carrier_on/_off link state tracking system.
With use_carrier enabled, bonding will always see these links as up,
regardless of their actual state.

	Additionally, other drivers do support netif_carrier, but do
not maintain it in real time, e.g., only polling the link state at
some fixed interval.  In this case, miimon will detect failures, but
only after some long period of time has expired.  If it appears that
miimon is very slow in detecting link failures, try specifying
use_carrier=0 to see if that improves the failure detection time.  If
it does, then it may be that the driver checks the carrier state at a
fixed interval, but does not cache the MII register values (so the
use_carrier=0 method of querying the registers directly works).  If
use_carrier=0 does not improve the failover, then the driver may cache
the registers, or the problem may be elsewhere.

	Also, remember that miimon only checks for the device's
carrier state.  It has no way to determine the state of devices on or
beyond other ports of a switch, or if a switch is refusing to pass
traffic while still maintaining carrier on.

9. SNMP agents
===============

	If running SNMP agents, the bonding driver should be loaded
before any network drivers participating in a bond.  This requirement
is due to the interface index (ipAdEntIfIndex) being associated to
the first interface found with a given IP address.  That is, there is
only one ipAdEntIfIndex for each IP address.  For example, if eth0 and
eth1 are slaves of bond0 and the driver for eth0 is loaded before the
bonding driver, the interface for the IP address will be associated
with the eth0 interface.  This configuration is shown below, the IP
address 192.168.1.1 has an interface index of 2 which indexes to eth0
in the ifDescr table (ifDescr.2).

     interfaces.ifTable.ifEntry.ifDescr.1 = lo
     interfaces.ifTable.ifEntry.ifDescr.2 = eth0
     interfaces.ifTable.ifEntry.ifDescr.3 = eth1
     interfaces.ifTable.ifEntry.ifDescr.4 = eth2
     interfaces.ifTable.ifEntry.ifDescr.5 = eth3
     interfaces.ifTable.ifEntry.ifDescr.6 = bond0
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 5
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 4
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1

	This problem is avoided by loading the bonding driver before
any network drivers participating in a bond.  Below is an example of
loading the bonding driver first, the IP address 192.168.1.1 is
correctly associated with ifDescr.2.

     interfaces.ifTable.ifEntry.ifDescr.1 = lo
     interfaces.ifTable.ifEntry.ifDescr.2 = bond0
     interfaces.ifTable.ifEntry.ifDescr.3 = eth0
     interfaces.ifTable.ifEntry.ifDescr.4 = eth1
     interfaces.ifTable.ifEntry.ifDescr.5 = eth2
     interfaces.ifTable.ifEntry.ifDescr.6 = eth3
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.10.10.10 = 6
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.192.168.1.1 = 2
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.10.74.20.94 = 5
     ip.ipAddrTable.ipAddrEntry.ipAdEntIfIndex.127.0.0.1 = 1

	While some distributions may not report the interface name in
ifDescr, the association between the IP address and IfIndex remains
and SNMP functions such as Interface_Scan_Next will report that
association.

10. Promiscuous mode
====================

	When running network monitoring tools, e.g., tcpdump, it is
common to enable promiscuous mode on the device, so that all traffic
is seen (instead of seeing only traffic destined for the local host).
The bonding driver handles promiscuous mode changes to the bonding
master device (e.g., bond0), and propagates the setting to the slave
devices.

	For the balance-rr, balance-xor, broadcast, and 802.3ad modes,
the promiscuous mode setting is propagated to all slaves.

	For the active-backup, balance-tlb and balance-alb modes, the
promiscuous mode setting is propagated only to the active slave.

	For balance-tlb mode, the active slave is the slave currently
receiving inbound traffic.

	For balance-alb mode, the active slave is the slave used as a
"primary."  This slave is used for mode-specific control traffic, for
sending to peers that are unassigned or if the load is unbalanced.

	For the active-backup, balance-tlb and balance-alb modes, when
the active slave changes (e.g., due to a link failure), the
promiscuous setting will be propagated to the new active slave.

11. Configuring Bonding for High Availability
=============================================

	High Availability refers to configurations that provide
maximum network availability by having redundant or backup devices,
links or switches between the host and the rest of the world.  The
goal is to provide the maximum availability of network connectivity
(i.e., the network always works), even though other configurations
could provide higher throughput.

11.1 High Availability in a Single Switch Topology
--------------------------------------------------

	If two hosts (or a host and a single switch) are directly
connected via multiple physical links, then there is no availability
penalty to optimizing for maximum bandwidth.  In this case, there is
only one switch (or peer), so if it fails, there is no alternative
access to fail over to.  Additionally, the bonding load balance modes
support link monitoring of their members, so if individual links fail,
the load will be rebalanced across the remaining devices.

	See Section 13, "Configuring Bonding for Maximum Throughput"
for information on configuring bonding with one peer device.

11.2 High Availability in a Multiple Switch Topology
----------------------------------------------------

	With multiple switches, the configuration of bonding and the
network changes dramatically.  In multiple switch topologies, there is
a trade off between network availability and usable bandwidth.

	Below is a sample network, configured to maximize the
availability of the network:

                |                                     |
                |port3                           port3|
          +-----+----+                          +-----+----+
          |          |port2       ISL      port2|          |
          | switch A +--------------------------+ switch B |
          |          |                          |          |
          +-----+----+                          +-----++---+
                |port1                           port1|
                |             +-------+               |
                +-------------+ host1 +---------------+
                         eth0 +-------+ eth1

	In this configuration, there is a link between the two
switches (ISL, or inter switch link), and multiple ports connecting to
the outside world ("port3" on each switch).  There is no technical
reason that this could not be extended to a third switch.

11.2.1 HA Bonding Mode Selection for Multiple Switch Topology
-------------------------------------------------------------

	In a topology such as the example above, the active-backup and
broadcast modes are the only useful bonding modes when optimizing for
availability; the other modes require all links to terminate on the
same peer for them to behave rationally.

active-backup: This is generally the preferred mode, particularly if
	the switches have an ISL and play together well.  If the
	network configuration is such that one switch is specifically
	a backup switch (e.g., has lower capacity, higher cost, etc),
	then the primary option can be used to insure that the
	preferred link is always used when it is available.

broadcast: This mode is really a special purpose mode, and is suitable
	only for very specific needs.  For example, if the two
	switches are not connected (no ISL), and the networks beyond
	them are totally independent.  In this case, if it is
	necessary for some specific one-way traffic to reach both
	independent networks, then the broadcast mode may be suitable.

11.2.2 HA Link Monitoring Selection for Multiple Switch Topology
----------------------------------------------------------------

	The choice of link monitoring ultimately depends upon your
switch.  If the switch can reliably fail ports in response to other
failures, then either the MII or ARP monitors should work.  For
example, in the above example, if the "port3" link fails at the remote
end, the MII monitor has no direct means to detect this.  The ARP
monitor could be configured with a target at the remote end of port3,
thus detecting that failure without switch support.

	In general, however, in a multiple switch topology, the ARP
monitor can provide a higher level of reliability in detecting end to
end connectivity failures (which may be caused by the failure of any
individual component to pass traffic for any reason).  Additionally,
the ARP monitor should be configured with multiple targets (at least
one for each switch in the network).  This will insure that,
regardless of which switch is active, the ARP monitor has a suitable
target to query.

	Note, also, that of late many switches now support a functionality
generally referred to as "trunk failover."  This is a feature of the
switch that causes the link state of a particular switch port to be set
down (or up) when the state of another switch port goes down (or up).
Its purpose is to propagate link failures from logically "exterior" ports
to the logically "interior" ports that bonding is able to monitor via
miimon.  Availability and configuration for trunk failover varies by
switch, but this can be a viable alternative to the ARP monitor when using
suitable switches.

12. Configuring Bonding for Maximum Throughput
==============================================

12.1 Maximizing Throughput in a Single Switch Topology
------------------------------------------------------

	In a single switch configuration, the best method to maximize
throughput depends upon the application and network environment.  The
various load balancing modes each have strengths and weaknesses in
different environments, as detailed below.

	For this discussion, we will break down the topologies into
two categories.  Depending upon the destination of most traffic, we
categorize them into either "gatewayed" or "local" configurations.

	In a gatewayed configuration, the "switch" is acting primarily
as a router, and the majority of traffic passes through this router to
other networks.  An example would be the following:


     +----------+                     +----------+
     |          |eth0            port1|          | to other networks
     | Host A   +---------------------+ router   +------------------->
     |          +---------------------+          | Hosts B and C are out
     |          |eth1            port2|          | here somewhere
     +----------+                     +----------+

	The router may be a dedicated router device, or another host
acting as a gateway.  For our discussion, the important point is that
the majority of traffic from Host A will pass through the router to
some other network before reaching its final destination.

	In a gatewayed network configuration, although Host A may
communicate with many other systems, all of its traffic will be sent
and received via one other peer on the local network, the router.

	Note that the case of two systems connected directly via
multiple physical links is, for purposes of configuring bonding, the
same as a gatewayed configuration.  In that case, it happens that all
traffic is destined for the "gateway" itself, not some other network
beyond the gateway.

	In a local configuration, the "switch" is acting primarily as
a switch, and the majority of traffic passes through this switch to
reach other stations on the same network.  An example would be the
following:

    +----------+            +----------+       +--------+
    |          |eth0   port1|          +-------+ Host B |
    |  Host A  +------------+  switch  |port3  +--------+
    |          +------------+          |                  +--------+
    |          |eth1   port2|          +------------------+ Host C |
    +----------+            +----------+port4             +--------+


	Again, the switch may be a dedicated switch device, or another
host acting as a gateway.  For our discussion, the important point is
that the majority of traffic from Host A is destined for other hosts
on the same local network (Hosts B and C in the above example).

	In summary, in a gatewayed configuration, traffic to and from
the bonded device will be to the same MAC level peer on the network
(the gateway itself, i.e., the router), regardless of its final
destination.  In a local configuration, traffic flows directly to and
from the final destinations, thus, each destination (Host B, Host C)
will be addressed directly by their individual MAC addresses.

	This distinction between a gatewayed and a local network
configuration is important because many of the load balancing modes
available use the MAC addresses of the local network source and
destination to make load balancing decisions.  The behavior of each
mode is described below.


12.1.1 MT Bonding Mode Selection for Single Switch Topology
-----------------------------------------------------------

	This configuration is the easiest to set up and to understand,
although you will have to decide which bonding mode best suits your
needs.  The trade offs for each mode are detailed below:

balance-rr: This mode is the only mode that will permit a single
	TCP/IP connection to stripe traffic across multiple
	interfaces. It is therefore the only mode that will allow a
	single TCP/IP stream to utilize more than one interface's
	worth of throughput.  This comes at a cost, however: the
	striping generally results in peer systems receiving packets out
	of order, causing TCP/IP's congestion control system to kick
	in, often by retransmitting segments.

	It is possible to adjust TCP/IP's congestion limits by
	altering the net.ipv4.tcp_reordering sysctl parameter.  The
	usual default value is 3, and the maximum useful value is 127.
	For a four interface balance-rr bond, expect that a single
	TCP/IP stream will utilize no more than approximately 2.3
	interface's worth of throughput, even after adjusting
	tcp_reordering.

	Note that the fraction of packets that will be delivered out of
	order is highly variable, and is unlikely to be zero.  The level
	of reordering depends upon a variety of factors, including the
	networking interfaces, the switch, and the topology of the
	configuration.  Speaking in general terms, higher speed network
	cards produce more reordering (due to factors such as packet
	coalescing), and a "many to many" topology will reorder at a
	higher rate than a "many slow to one fast" configuration.

	Many switches do not support any modes that stripe traffic
	(instead choosing a port based upon IP or MAC level addresses);
	for those devices, traffic for a particular connection flowing
	through the switch to a balance-rr bond will not utilize greater
	than one interface's worth of bandwidth.

	If you are utilizing protocols other than TCP/IP, UDP for
	example, and your application can tolerate out of order
	delivery, then this mode can allow for single stream datagram
	performance that scales near linearly as interfaces are added
	to the bond.

	This mode requires the switch to have the appropriate ports
	configured for "etherchannel" or "trunking."

active-backup: There is not much advantage in this network topology to
	the active-backup mode, as the inactive backup devices are all
	connected to the same peer as the primary.  In this case, a
	load balancing mode (with link monitoring) will provide the
	same level of network availability, but with increased
	available bandwidth.  On the plus side, active-backup mode
	does not require any configuration of the switch, so it may
	have value if the hardware available does not support any of
	the load balance modes.

balance-xor: This mode will limit traffic such that packets destined
	for specific peers will always be sent over the same
	interface.  Since the destination is determined by the MAC
	addresses involved, this mode works best in a "local" network
	configuration (as described above), with destinations all on
	the same local network.  This mode is likely to be suboptimal
	if all your traffic is passed through a single router (i.e., a
	"gatewayed" network configuration, as described above).

	As with balance-rr, the switch ports need to be configured for
	"etherchannel" or "trunking."

broadcast: Like active-backup, there is not much advantage to this
	mode in this type of network topology.

802.3ad: This mode can be a good choice for this type of network
	topology.  The 802.3ad mode is an IEEE standard, so all peers
	that implement 802.3ad should interoperate well.  The 802.3ad
	protocol includes automatic configuration of the aggregates,
	so minimal manual configuration of the switch is needed
	(typically only to designate that some set of devices is
	available for 802.3ad).  The 802.3ad standard also mandates
	that frames be delivered in order (within certain limits), so
	in general single connections will not see misordering of
	packets.  The 802.3ad mode does have some drawbacks: the
	standard mandates that all devices in the aggregate operate at
	the same speed and duplex.  Also, as with all bonding load
	balance modes other than balance-rr, no single connection will
	be able to utilize more than a single interface's worth of
	bandwidth.  

	Additionally, the linux bonding 802.3ad implementation
	distributes traffic by peer (using an XOR of MAC addresses),
	so in a "gatewayed" configuration, all outgoing traffic will
	generally use the same device.  Incoming traffic may also end
	up on a single device, but that is dependent upon the
	balancing policy of the peer's 8023.ad implementation.  In a
	"local" configuration, traffic will be distributed across the
	devices in the bond.

	Finally, the 802.3ad mode mandates the use of the MII monitor,
	therefore, the ARP monitor is not available in this mode.

balance-tlb: The balance-tlb mode balances outgoing traffic by peer.
	Since the balancing is done according to MAC address, in a
	"gatewayed" configuration (as described above), this mode will
	send all traffic across a single device.  However, in a
	"local" network configuration, this mode balances multiple
	local network peers across devices in a vaguely intelligent
	manner (not a simple XOR as in balance-xor or 802.3ad mode),
	so that mathematically unlucky MAC addresses (i.e., ones that
	XOR to the same value) will not all "bunch up" on a single
	interface.

	Unlike 802.3ad, interfaces may be of differing speeds, and no
	special switch configuration is required.  On the down side,
	in this mode all incoming traffic arrives over a single
	interface, this mode requires certain ethtool support in the
	network device driver of the slave interfaces, and the ARP
	monitor is not available.

balance-alb: This mode is everything that balance-tlb is, and more.
	It has all of the features (and restrictions) of balance-tlb,
	and will also balance incoming traffic from local network
	peers (as described in the Bonding Module Options section,
	above).

	The only additional down side to this mode is that the network
	device driver must support changing the hardware address while
	the device is open.

12.1.2 MT Link Monitoring for Single Switch Topology
----------------------------------------------------

	The choice of link monitoring may largely depend upon which
mode you choose to use.  The more advanced load balancing modes do not
support the use of the ARP monitor, and are thus restricted to using
the MII monitor (which does not provide as high a level of end to end
assurance as the ARP monitor).

12.2 Maximum Throughput in a Multiple Switch Topology
-----------------------------------------------------

	Multiple switches may be utilized to optimize for throughput
when they are configured in parallel as part of an isolated network
between two or more systems, for example:

                       +-----------+
                       |  Host A   | 
                       +-+---+---+-+
                         |   |   |
                +--------+   |   +---------+
                |            |             |
         +------+---+  +-----+----+  +-----+----+
         | Switch A |  | Switch B |  | Switch C |
         +------+---+  +-----+----+  +-----+----+
                |            |             |
                +--------+   |   +---------+
                         |   |   |
                       +-+---+---+-+
                       |  Host B   | 
                       +-----------+

	In this configuration, the switches are isolated from one
another.  One reason to employ a topology such as this is for an
isolated network with many hosts (a cluster configured for high
performance, for example), using multiple smaller switches can be more
cost effective than a single larger switch, e.g., on a network with 24
hosts, three 24 port switches can be significantly less expensive than
a single 72 port switch.

	If access beyond the network is required, an individual host
can be equipped with an additional network device connected to an
external network; this host then additionally acts as a gateway.

12.2.1 MT Bonding Mode Selection for Multiple Switch Topology
-------------------------------------------------------------

	In actual practice, the bonding mode typically employed in
configurations of this type is balance-rr.  Historically, in this
network configuration, the usual caveats about out of order packet
delivery are mitigated by the use of network adapters that do not do
any kind of packet coalescing (via the use of NAPI, or because the
device itself does not generate interrupts until some number of
packets has arrived).  When employed in this fashion, the balance-rr
mode allows individual connections between two hosts to effectively
utilize greater than one interface's bandwidth.

12.2.2 MT Link Monitoring for Multiple Switch Topology
------------------------------------------------------

	Again, in actual practice, the MII monitor is most often used
in this configuration, as performance is given preference over
availability.  The ARP monitor will function in this topology, but its
advantages over the MII monitor are mitigated by the volume of probes
needed as the number of systems involved grows (remember that each
host in the network is configured with bonding).

13. Switch Behavior Issues
==========================

13.1 Link Establishment and Failover Delays
-------------------------------------------

	Some switches exhibit undesirable behavior with regard to the
timing of link up and down reporting by the switch.

	First, when a link comes up, some switches may indicate that
the link is up (carrier available), but not pass traffic over the
interface for some period of time.  This delay is typically due to
some type of autonegotiation or routing protocol, but may also occur
during switch initialization (e.g., during recovery after a switch
failure).  If you find this to be a problem, specify an appropriate
value to the updelay bonding module option to delay the use of the
relevant interface(s).

	Second, some switches may "bounce" the link state one or more
times while a link is changing state.  This occurs most commonly while
the switch is initializing.  Again, an appropriate updelay value may
help.

	Note that when a bonding interface has no active links, the
driver will immediately reuse the first link that goes up, even if the
updelay parameter has been specified (the updelay is ignored in this
case).  If there are slave interfaces waiting for the updelay timeout
to expire, the interface that first went into that state will be
immediately reused.  This reduces down time of the network if the
value of updelay has been overestimated, and since this occurs only in
cases with no connectivity, there is no additional penalty for
ignoring the updelay.

	In addition to the concerns about switch timings, if your
switches take a long time to go into backup mode, it may be desirable
to not activate a backup interface immediately after a link goes down.
Failover may be delayed via the downdelay bonding module option.

13.2 Duplicated Incoming Packets
--------------------------------

	NOTE: Starting with version 3.0.2, the bonding driver has logic to
suppress duplicate packets, which should largely eliminate this problem.
The following description is kept for reference.

	It is not uncommon to observe a short burst of duplicated
traffic when the bonding device is first used, or after it has been
idle for some period of time.  This is most easily observed by issuing
a "ping" to some other host on the network, and noticing that the
output from ping flags duplicates (typically one per slave).

	For example, on a bond in active-backup mode with five slaves
all connected to one switch, the output may appear as follows:

# ping -n 10.0.4.2
PING 10.0.4.2 (10.0.4.2) from 10.0.3.10 : 56(84) bytes of data.
64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.7 ms
64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
64 bytes from 10.0.4.2: icmp_seq=1 ttl=64 time=13.8 ms (DUP!)
64 bytes from 10.0.4.2: icmp_seq=2 ttl=64 time=0.216 ms
64 bytes from 10.0.4.2: icmp_seq=3 ttl=64 time=0.267 ms
64 bytes from 10.0.4.2: icmp_seq=4 ttl=64 time=0.222 ms

	This is not due to an error in the bonding driver, rather, it
is a side effect of how many switches update their MAC forwarding
tables.  Initially, the switch does not associate the MAC address in
the packet with a particular switch port, and so it may send the
traffic to all ports until its MAC forwarding table is updated.  Since
the interfaces attached to the bond may occupy multiple ports on a
single switch, when the switch (temporarily) floods the traffic to all
ports, the bond device receives multiple copies of the same packet
(one per slave device).

	The duplicated packet behavior is switch dependent, some
switches exhibit this, and some do not.  On switches that display this
behavior, it can be induced by clearing the MAC forwarding table (on
most Cisco switches, the privileged command "clear mac address-table
dynamic" will accomplish this).

14. Hardware Specific Considerations
====================================

	This section contains additional information for configuring
bonding on specific hardware platforms, or for interfacing bonding
with particular switches or other devices.

14.1 IBM BladeCenter
--------------------

	This applies to the JS20 and similar systems.

	On the JS20 blades, the bonding driver supports only
balance-rr, active-backup, balance-tlb and balance-alb modes.  This is
largely due to the network topology inside the BladeCenter, detailed
below.

JS20 network adapter information
--------------------------------

	All JS20s come with two Broadcom Gigabit Ethernet ports
integrated on the planar (that's "motherboard" in IBM-speak).  In the
BladeCenter chassis, the eth0 port of all JS20 blades is hard wired to
I/O Module #1; similarly, all eth1 ports are wired to I/O Module #2.
An add-on Broadcom daughter card can be installed on a JS20 to provide
two more Gigabit Ethernet ports.  These ports, eth2 and eth3, are
wired to I/O Modules 3 and 4, respectively.

	Each I/O Module may contain either a switch or a passthrough
module (which allows ports to be directly connected to an external
switch).  Some bonding modes require a specific BladeCenter internal
network topology in order to function; these are detailed below.

	Additional BladeCenter-specific networking information can be
found in two IBM Redbooks (www.ibm.com/redbooks):

"IBM eServer BladeCenter Networking Options"
"IBM eServer BladeCenter Layer 2-7 Network Switching"

BladeCenter networking configuration
------------------------------------

	Because a BladeCenter can be configured in a very large number
of ways, this discussion will be confined to describing basic
configurations.

	Normally, Ethernet Switch Modules (ESMs) are used in I/O
modules 1 and 2.  In this configuration, the eth0 and eth1 ports of a
JS20 will be connected to different internal switches (in the
respective I/O modules).

	A passthrough module (OPM or CPM, optical or copper,
passthrough module) connects the I/O module directly to an external
switch.  By using PMs in I/O module #1 and #2, the eth0 and eth1
interfaces of a JS20 can be redirected to the outside world and
connected to a common external switch.

	Depending upon the mix of ESMs and PMs, the network will
appear to bonding as either a single switch topology (all PMs) or as a
multiple switch topology (one or more ESMs, zero or more PMs).  It is
also possible to connect ESMs together, resulting in a configuration
much like the example in "High Availability in a Multiple Switch
Topology," above.

Requirements for specific modes
-------------------------------

	The balance-rr mode requires the use of passthrough modules
for devices in the bond, all connected to an common external switch.
That switch must be configured for "etherchannel" or "trunking" on the
appropriate ports, as is usual for balance-rr.

	The balance-alb and balance-tlb modes will function with
either switch modules or passthrough modules (or a mix).  The only
specific requirement for these modes is that all network interfaces
must be able to reach all destinations for traffic sent over the
bonding device (i.e., the network must converge at some point outside
the BladeCenter).

	The active-backup mode has no additional requirements.

Link monitoring issues
----------------------

	When an Ethernet Switch Module is in place, only the ARP
monitor will reliably detect link loss to an external switch.  This is
nothing unusual, but examination of the BladeCenter cabinet would
suggest that the "external" network ports are the ethernet ports for
the system, when it fact there is a switch between these "external"
ports and the devices on the JS20 system itself.  The MII monitor is
only able to detect link failures between the ESM and the JS20 system.

	When a passthrough module is in place, the MII monitor does
detect failures to the "external" port, which is then directly
connected to the JS20 system.

Other concerns
--------------

	The Serial Over LAN (SoL) link is established over the primary
ethernet (eth0) only, therefore, any loss of link to eth0 will result
in losing your SoL connection.  It will not fail over with other
network traffic, as the SoL system is beyond the control of the
bonding driver.

	It may be desirable to disable spanning tree on the switch
(either the internal Ethernet Switch Module, or an external switch) to
avoid fail-over delay issues when using bonding.

	
15. Frequently Asked Questions
==============================

1.  Is it SMP safe?

	Yes. The old 2.0.xx channel bonding patch was not SMP safe.
The new driver was designed to be SMP safe from the start.

2.  What type of cards will work with it?

	Any Ethernet type cards (you can even mix cards - a Intel
EtherExpress PRO/100 and a 3com 3c905b, for example).  For most modes,
devices need not be of the same speed.

	Starting with version 3.2.1, bonding also supports Infiniband
slaves in active-backup mode.

3.  How many bonding devices can I have?

	There is no limit.

4.  How many slaves can a bonding device have?

	This is limited only by the number of network interfaces Linux
supports and/or the number of network cards you can place in your
system.

5.  What happens when a slave link dies?

	If link monitoring is enabled, then the failing device will be
disabled.  The active-backup mode will fail over to a backup link, and
other modes will ignore the failed link.  The link will continue to be
monitored, and should it recover, it will rejoin the bond (in whatever
manner is appropriate for the mode). See the sections on High
Availability and the documentation for each mode for additional
information.
	
	Link monitoring can be enabled via either the miimon or
arp_interval parameters (described in the module parameters section,
above).  In general, miimon monitors the carrier state as sensed by
the underlying network device, and the arp monitor (arp_interval)
monitors connectivity to another host on the local network.

	If no link monitoring is configured, the bonding driver will
be unable to detect link failures, and will assume that all links are
always available.  This will likely result in lost packets, and a
resulting degradation of performance.  The precise performance loss
depends upon the bonding mode and network configuration.

6.  Can bonding be used for High Availability?

	Yes.  See the section on High Availability for details.

7.  Which switches/systems does it work with?

	The full answer to this depends upon the desired mode.

	In the basic balance modes (balance-rr and balance-xor), it
works with any system that supports etherchannel (also called
trunking).  Most managed switches currently available have such
support, and many unmanaged switches as well.

	The advanced balance modes (balance-tlb and balance-alb) do
not have special switch requirements, but do need device drivers that
support specific features (described in the appropriate section under
module parameters, above).

	In 802.3ad mode, it works with systems that support IEEE
802.3ad Dynamic Link Aggregation.  Most managed and many unmanaged
switches currently available support 802.3ad.

        The active-backup mode should work with any Layer-II switch.

8.  Where does a bonding device get its MAC address from?

	When using slave devices that have fixed MAC addresses, or when
the fail_over_mac option is enabled, the bonding device's MAC address is
the MAC address of the active slave.

	For other configurations, if not explicitly configured (with
ifconfig or ip link), the MAC address of the bonding device is taken from
its first slave device.  This MAC address is then passed to all following
slaves and remains persistent (even if the first slave is removed) until
the bonding device is brought down or reconfigured.

	If you wish to change the MAC address, you can set it with
ifconfig or ip link:

# ifconfig bond0 hw ether 00:11:22:33:44:55

# ip link set bond0 address 66:77:88:99:aa:bb

	The MAC address can be also changed by bringing down/up the
device and then changing its slaves (or their order):

# ifconfig bond0 down ; modprobe -r bonding
# ifconfig bond0 .... up
# ifenslave bond0 eth...

	This method will automatically take the address from the next
slave that is added.

	To restore your slaves' MAC addresses, you need to detach them
from the bond (`ifenslave -d bond0 eth0'). The bonding driver will
then restore the MAC addresses that the slaves had before they were
enslaved.

16. Resources and Links
=======================

	The latest version of the bonding driver can be found in the latest
version of the linux kernel, found on http://kernel.org

	The latest version of this document can be found in the latest kernel
source (named Documentation/networking/bonding.txt).

	Discussions regarding the usage of the bonding driver take place on the
bonding-devel mailing list, hosted at sourceforge.net. If you have questions or
problems, post them to the list.  The list address is:

[email protected]

	The administrative interface (to subscribe or unsubscribe) can
be found at:

https://lists.sourceforge.net/lists/listinfo/bonding-devel

	Discussions regarding the developpement of the bonding driver take place
on the main Linux network mailing list, hosted at vger.kernel.org. The list
address is:

[email protected]

	The administrative interface (to subscribe or unsubscribe) can
be found at:

http://vger.kernel.org/vger-lists.html#netdev

Donald Becker's Ethernet Drivers and diag programs may be found at :
 - http://web.archive.org/web/*/http://www.scyld.com/network/ 

You will also find a lot of information regarding Ethernet, NWay, MII,
etc. at www.scyld.com.

-- END --

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